Document and Entity Information	3 Months Ended
Document and Entity Information	Mar. 31, 2011	May 02, 2011
Document and Entity Information
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2011
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	Q1
Trading Symbol	PXD
Entity Registrant Name	PIONEER NATURAL RESOURCES CO
Entity Central Index Key	0001038357
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		116,755,591

Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2011	Dec. 31, 2010
Current assets:
Cash and cash equivalents	$ 520,651	$ 111,160
Accounts receivable:
Trade, net of allowance for doubtful accounts of $1,171 and $1,155 as of March 31, 2011 and December 31, 2010, respectively	276,338	237,511
Due from affiliates	955	7,792
Income taxes receivable	30,900	30,901
Inventories	187,715	173,615
Prepaid expenses	10,010	11,441
Deferred income taxes	22,802	156,650
Discontinued operations held for sale		281,741
Other current assets:
Derivatives	147,643	171,679
Other	38,579	14,693
Total current assets	1,235,593	1,197,183
Oil and gas properties, using the successful efforts method of accounting:
Proved properties	11,069,563	10,739,114
Unproved properties	200,209	191,112
Accumulated depletion, depreciation and amortization	(3,495,838)	(3,366,440)
Total property, plant and equipment	7,773,934	7,563,786
Goodwill	298,145	298,182
Other property and equipment, net	380,376	283,542
Other assets:
Investment in unconsolidated affiliate	109,391	72,045
Derivatives	106,210	151,011
Other, net of allowance for doubtful accounts of $2,364 and $2,519 as of March 31, 2011 and December 31, 2010, respectively	122,337	113,353
Assets, Total	10,025,986	9,679,102
Accounts payable:
Trade	350,030	354,890
Due to affiliates	19,303	64,260
Interest payable	33,942	59,008
Income taxes payable	33,072	19,168
Deferred income taxes		1,144
Discontinued operations held for sale		108,592
Other current liabilities:
Derivatives	173,628	80,997
Deferred revenue	44,327	44,951
Other	41,562	36,210
Total current liabilities	695,864	769,220
Long-term debt	2,562,688	2,601,670
Derivatives	179,914	56,574
Deferred income taxes	1,763,976	1,751,310
Deferred revenue	31,610	42,069
Other liabilities	238,367	232,234
Stockholders' equity:
Common stock, $.01 par value; 500,000,000 shares authorized; 127,469,647 and 126,212,256 shares issued at March 31, 2011 and December 31, 2010, respectively	1,275	1,262
Additional paid-in capital	3,060,249	3,022,768
Treasury stock, at cost: 11,276,450 and 10,903,743 at March 31, 2011 and December 31, 2010, respectively	(456,359)	(421,235)
Retained earnings	1,854,041	1,510,427
Accumulated other comprehensive income - deferred hedge gains, net of tax	3,439	7,361
Total stockholders' equity attributable to common stockholders	4,462,645	4,120,583
Noncontrolling interests in consolidating subsidiaries	90,922	105,442
Total stockholders' equity	4,553,567	4,226,025
Commitments and contingencies
Liabilities and Stockholders' Equity, Total	$ 10,025,986	$ 9,679,102

Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Mar. 31, 2011	Dec. 31, 2010
Consolidated Balance Sheets
Trade, allowance for doubtful accounts	$ 1,171	$ 1,155
Other, allowance for doubtful accounts	$ 2,364	$ 2,519
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	127,469,647	126,212,256
Treasury stock, shares	11,276,450	10,903,743

Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2011	Mar. 31, 2010
Revenues and other income:
Oil and gas	$ 497,130	$ 472,045
Interest and other	32,687	18,008
Gain (loss) on disposition of assets, net	(2,191)	16,943
Revenues and other income	527,626	506,996
Costs and expenses:
Oil and gas production	99,931	86,100
Production and ad valorem taxes	33,296	27,061
Depletion, depreciation and amortization	140,373	144,428
Exploration and abandonments	17,643	16,848
General and administrative	44,106	38,315
Accretion of discount on asset retirement obligations	2,655	2,859
Interest	45,227	47,523
Hurricane activity, net	71	(7,410)
Derivative (gains) losses, net	244,432	(265,476)
Other	17,881	15,946
Costs and expenses, Total	645,615	106,194
Income (loss) from continuing operations before income taxes	(117,989)	400,802
Income tax benefit (provision)	47,151	(144,007)
Income (loss) from continuing operations	(70,838)	256,795
Income from discontinued operations, net of tax	414,642	3,811
Net income	343,804	260,606
Net (income) loss attributable to the noncontrolling interests	4,790	(15,352)
Net income attributable to common stockholders	348,594	245,254
Basic earnings per share:
Income (loss) from continuing operations attributable to common stockholders	$ (0.57)	$ 2.06
Income from discontinued operations attributable to common stockholders	$ 3.53	$ 0.03
Net income attributable to common stockholders	$ 2.96	$ 2.09
Diluted earnings per share:
Income (loss) from continuing operations attributable to common stockholders	$ (0.57)	$ 2.05
Income from discontinued operations attributable to common stockholders	$ 3.53	$ 0.03
Net income attributable to common stockholders	$ 2.96	$ 2.08
Weighted average shares outstanding:
Basic	115,869	114,655
Diluted	115,869	115,462
Dividends declared per share	$ 0.04	$ 0.04
Amounts attributable to common stockholders:
Income (loss) from continuing operations	(66,048)	241,443
Income from discontinued operations, net of tax	414,642	3,811
Net income	$ 348,594	$ 245,254

Consolidated Statement of Stockholders' Equity (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income [Member]	Noncontrolling Interests [Member]
Beginning Balance at Dec. 31, 2010	$ 4,226,025	$ 1,262	$ 3,022,768	$ (421,235)	$ 1,510,427	$ 7,361	$ 105,442
Beginning Balance (in shares) at Dec. 31, 2010		115,309,000
Dividends declared ($0.04 per share)	(4,759)				(4,759)
Exercise of long-term incentive plan stock options (in shares)		14,000
Exercise of long-term incentive plan stock options	337			558	(221)
Treasury stock purchases (in shares)		(387,000)
Treasury stock purchases	(35,682)			(35,682)
Tax benefit related to stock-based compensation	28,083		28,083
Disposition of subsidiary	(508)		(508)
Compensation costs:
Vested compensation awards, net (in shares)		1,257,000
Vested compensation awards, net		13	(13)
Compensation costs included in net income	10,239		9,919				320
Cash distributions to noncontrolling interests	(6,664)						(6,664)
Net income (loss)	343,804				348,594		(4,790)
Deferred hedging activity, net of tax:
Net hedge gains included in continuing operations	(7,308)					(3,922)	(3,386)
Ending Balance at Mar. 31, 2011	$ 4,553,567	$ 1,275	$ 3,060,249	$ (456,359)	$ 1,854,041	$ 3,439	$ 90,922
Ending Balance (in shares) at Mar. 31, 2011		116,193,000

Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2011	Mar. 31, 2010
Cash flows from operating activities:
Net income	$ 343,804	$ 260,606
Adjustments to reconcile net income to net cash provided by operating activities:
Depletion, depreciation and amortization	140,373	144,428
Exploration expenses, including dry holes	1,481	3,587
Deferred income taxes	(55,868)	141,545
(Gain) loss on disposition of assets, net	2,191	(16,943)
Accretion of discount on asset retirement obligations	2,655	2,859
Discontinued operations	(408,065)	21,558
Interest expense	7,637	7,408
Derivative related activity	276,683	(281,871)
Amortization of stock-based compensation	10,174	9,624
Amortization of deferred revenue	(11,083)	(22,483)
Other noncash items	(20,488)	(403)
Change in operating assets and liabilities
Accounts receivable, net	(25,270)	48,080
Income taxes receivable	1	21,264
Inventories	(29,319)	17,429
Prepaid expenses	1,342	435
Other current assets	3,305	1,226
Accounts payable	(89,980)	(34,296)
Interest payable	(25,066)	(13,314)
Income taxes payable	15,354	(1,536)
Other current liabilities	3,353	(9,840)
Net cash provided by operating activities	143,214	299,363
Cash flows from investing activities:
Proceeds from disposition of assets, net of cash sold	810,470	34,985
Investment in unconsolidated subsidiary	(37,048)
Additions to oil and gas properties	(309,974)	(156,529)
Additions to other assets and other property and equipment, net	(129,280)	(44,999)
Net cash provided by (used in) investing activities	334,168	(166,543)
Cash flows from financing activities:
Borrowings under long-term debt	60,610	87,154
Principal payments on long-term debt	(105,810)	(206,264)
Contributions from noncontrolling interests		1,151
Distributions to noncontrolling interests	(6,664)	(6,605)
Borrowings (payments) of other liabilities	(20)	2,818
Exercise of long-term incentive plan stock options	337	2,583
Purchases of treasury stock	(35,682)	(12,978)
Excess tax benefits from share-based payment arrangements	28,083	6,705
Payment of financing fees	(8,672)	(147)
Dividends paid	(73)	(65)
Net cash used in financing activities	(67,891)	(125,648)
Net increase in cash and cash equivalents	409,491	7,172
Cash and cash equivalents, beginning of period	111,160	27,368
Cash and cash equivalents, end of period	$ 520,651	$ 34,540

Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2011	Mar. 31, 2010
Consolidated Statements of Comprehensive Income
Net income	$ 343,804	$ 260,606
Other comprehensive loss:
Net hedge gains included in continuing operations	(8,056)	(20,926)
Income tax provision	748	5,035
Other comprehensive loss	(7,308)	(15,891)
Comprehensive income	336,496	244,715
Comprehensive (income) loss attributable to the noncontrolling interests	8,176	(11,036)
Comprehensive income attributable to common stockholders	$ 344,672	$ 233,679

Organization and Nature of Operations	3 Months Ended
Organization and Nature of Operations	Mar. 31, 2011
Organization and Nature of Operations
Organization and Nature of Operations	NOTE A. Organization and Nature of Operations Pioneer Natural Resources Company ("Pioneer" or the "Company") is a Delaware corporation whose common stock is listed and traded on the New York Stock Exchange. The Company is a large independent oil and gas exploration and production company with continuing operations in the United States and South Africa.

- Definition

Description containing the entire organization, consolidation and basis of presentation of financial statements disclosure. May be provided in more than one note to the financial statements, as long as users are provided with an understanding of (1) the significant judgments and assumptions made by an enterprise in determining whether it must consolidate a VIE and/or disclose information about its involvement with a VIE, (2) the nature of restrictions on a consolidated VIE's assets reported by an enterprise in its statement of financial position, including the carrying amounts of such assets, (3) the nature of, and changes in, the risks associated with an enterprise's involvement with the VIE, and (4) how an enterprise's involvement with the VIE affects the enterprise's financial position, financial performance, and cash flows. Describes procedure if disclosures are provided in more than one note to the financial statements.

+ References+ Details

Basis of Presentation

3 Months Ended

Mar. 31, 2011

Basis of Presentation

Basis of Presentation

NOTE B. Basis of Presentation

Presentation. In the opinion of management, the consolidated financial statements of the Company as of March 31, 2011 and for the three months ended March 31, 2011 and 2010 include all adjustments and accruals, consisting only of normal recurring accrual adjustments, which are necessary for a fair presentation of the results for the interim periods. These interim results are not necessarily indicative of results for a full year.

Certain information and footnote disclosures normally included in financial statements prepared in accordance with generally accepted accounting principles in the United States ("GAAP") have been condensed or omitted in this report pursuant to the rules and regulations of the United States Securities and Exchange Commission (the "SEC"). These consolidated financial statements should be read in connection with the consolidated financial statements and notes thereto included in the Company's Annual Report on Form 10-K for the year ended December 31, 2010.

Discontinued operations. During December 2010, the Company committed to a plan to divest 100 percent of the Company's share holdings in Pioneer Natural Resources Tunisia Ltd. and Pioneer Natural Resources Anaguid Ltd. (referred to in the aggregate as "Pioneer Tunisia"). In February 2011, the Company completed the sale of Pioneer Tunisia to an unaffiliated third party. Accordingly, the Company classified the assets and liabilities of Pioneer Tunisia as discontinued operations held for sale in the accompanying balance sheet as of December 31, 2010 and has classified the results of operations of Pioneer Tunisia as discontinued operations, net of tax for the three months ended March 31, 2011 and 2010 in the accompanying consolidated statements of operations (representing a recasting of the Pioneer Tunisia results of operations for the three months ended March 31, 2010, which were originally classified as continuing operations). See Note Q for more information regarding the sale of Pioneer Tunisia.

Allowances for doubtful accounts. As of March 31, 2011 and December 31, 2010, the Company's allowances for doubtful accounts totaled $3.5 million and $3.7 million, respectively. Changes in the Company's allowance for doubtful accounts during the three months ended March 31, 2011 are summarized in the following table:


	Three Months Ended March 31, 2011
	(in thousands)

Beginning allowance for doubtful accounts balance	$	3,674
Amount recorded in other expense for bad debt expense		18
Other net decreases		(157	)


Ending allowance for doubtful accounts balance	$	3,535

Inventories. Inventories used in continuing operations consisted of $206.8 million and $183.4 million of materials and supplies and $3.8 million and $3.9 million of commodities as of March 31, 2011 and December 31, 2010, respectively. As of March 31, 2011 and December 31, 2010, the Company's materials and supplies inventory was net of $3.8 million and $3.6 million, respectively, of valuation reserve allowances. As of March 31, 2011 and December 31, 2010, the Company estimated that $22.9 million and $13.7 million, respectively, of its materials and supplies inventory would not be utilized or sold within one year. Accordingly, those inventory values have been classified as other noncurrent assets in the accompanying consolidated balance sheets. As of December 31, 2010, the Company also had inventory in Tunisia totaling $13.6 million that is classified as discontinued operations held for sale in the accompanying consolidated balance sheet as of December 31, 2010.

Derivatives and hedging. All derivatives are recorded on the accompanying consolidated balance sheets at estimated fair value. See Note D for further information regarding the fair value of the Company's derivatives. Effective February 1, 2009, the Company discontinued hedge accounting on all of its then-existing hedge contracts. Changes in the fair value of effective cash flow hedges prior to the Company's discontinuance of hedge accounting were recorded as a component of accumulated other comprehensive income – deferred hedge gains, net of tax ("AOCI – Hedging"), in the stockholders' equity section of the accompanying consolidated balance sheets, and are being transferred to earnings during the same periods in which the hedged transactions are recognized in the Company's earnings. Since February 1, 2009, the Company has recognized all changes in the fair values of its derivative contracts as gains or losses in the earnings of the periods in which they occur.

The Company classifies the fair value amounts of derivative assets and liabilities executed under master netting arrangements as net current or noncurrent derivative assets or net current or noncurrent derivative liabilities, whichever the case may be, by commodity and master netting counterparty. Net derivative asset values are determined, in part, by utilization of the derivative counterparties' credit-adjusted risk-free rate curves and net derivative liabilities are determined, in part, by utilization of the Company's and Pioneer Southwest Energy Partners L.P.'s ("Pioneer Southwest," a majority-owned and consolidated subsidiary) credit-adjusted risk-free rate curves. The credit-adjusted risk-free rate curves for the Company and the counterparties are based on their independent market-quoted credit default swap rate curves plus the United States Treasury Bill yield curve as of the valuation date. Pioneer Southwest's credit-adjusted risk-free rate curve is based on independent market-quoted forward London Interbank Offered Rate ("LIBOR") curves plus 250 basis points, representing Pioneer Southwest's estimated borrowing rate.

Goodwill. Goodwill is assessed for impairment whenever events or circumstances indicate that impairment of the carrying value of goodwill is likely, but no less often than annually. If the carrying value of goodwill is determined to be impaired, it is reduced for the impaired value with a corresponding charge to pretax earnings in the period in which it is determined to be impaired. During the third quarter of 2010, the Company performed its annual assessment of goodwill impairment and determined that there was no impairment.

Noncontrolling interest in consolidated subsidiaries. The Company owns a 0.1 percent general partner interest and a 61.9 percent limited partner interest in Pioneer Southwest. Pioneer Southwest owns interests in certain oil and gas properties in the Spraberry field in the Permian Basin of West Texas. The financial position, results of operations and cash flows of Pioneer Southwest are consolidated with those of the Company.

The Company also owns a majority interest in Sendero Drilling Company, LLC ("Sendero"), which owns and operates land-based drilling rigs in the United States. As of March 31, 2011, Sendero owned 14 drilling rigs operating, or being readied to operate, under contracts to the Company in the Spraberry field. In addition, the Company owns the majority interests in certain other subsidiaries with operations in the United States.

Noncontrolling interest in the net assets of consolidated subsidiaries totaled $90.9 million and $105.4 million as of March 31, 2011 and December 31, 2010, respectively. The Company recorded a net loss attributable to the noncontrolling interests of $4.8 million for the three months ended March 31, 2011 (principally related to Pioneer Southwest), compared to net income attributable to the noncontrolling interests of $15.4 million for the three months ended March 31, 2010. The net loss attributable to noncontrolling interests for the first quarter of 2011 was primarily due to noncash mark-to-market derivative losses recorded by Pioneer Southwest during the three months ended March 31, 2011.

Investment in unconsolidated affiliate. The Company owns a 50.1 percent interest in EFS Midstream LLC ("EFS Midstream"), which owns and operates natural gas and liquids gathering, treating and transportation assets in the Eagle Ford Shale area of South Texas.

The Company accounts for the EFS Midstream investment under the equity method of accounting for investments in unconsolidated affiliates. Under the equity method, the Company's investment in unconsolidated affiliates is increased for investments made and the investor's share of the investee's net income, and decreased for distributions received, the carrying value of investor's interests sold and the investor's share of the investee's net losses. The Company's equity interest in the net income of EFS Midstream is recorded in interest and other income in the Company's accompanying consolidated statements of operations.

Stock-based compensation. For stock-based compensation equity awards granted or modified, compensation expense is being recognized in the Company's financial statements on a straight line basis over the awards' vesting periods based on their fair values on the dates of grant. The amount of compensation expense recognized at any date is at least equal to the portion of the grant-date value of the award that is vested at that date. The Company utilizes (i) the Black-Scholes option pricing model to measure the fair value of stock options, (ii) the prior day's closing stock price on the date of grant for the fair value of restricted stock or unit awards and phantom unit awards that are expected to be settled wholly in the Company's common stock or Pioneer Southwest common units ("Equity Awards"), (iii) the Monte Carlo simulation method for the fair value of performance unit awards and (iv) a probabilistic forecasted fair value method for series B unit awards issued by Sendero.

Stock-based compensation liability awards are awards that are expected to be settled wholly or partially in cash on their vesting dates, rather than in shares or units ("Liability Awards"). Stock-based Liability Awards are recorded as accounts payable – affiliates based on the fair value of the services that have been rendered on the unvested portions of the awards on the balance sheet date. The fair values of Liability Awards are updated at each balance sheet date and changes in the fair values of the unvested portions of the awards for which services have been rendered are recorded as increases or decreases to compensation expense. As of March 31, 2011, accounts payable – affiliates includes $1.6 million of liabilities attributable to the Liability Awards.

For the three months ended March 31, 2011, the Company recorded $13.0 million of stock-based compensation costs for all plans, as compared to $9.8 million for the same period of 2010. As of March 31, 2011, there was $109.1 million of unrecognized compensation expense related to unvested share- and unit-based compensation plan awards, including $28.0 million attributable to Liability Awards. This compensation will be recognized over the remaining vesting periods of the awards, which on a weighted average basis is a period of less than three years.

The Company's issued shares, as reflected in the consolidated balance sheets at March 31, 2011 and December 31, 2010, do not include 566,389 and 825,796 common shares, respectively, associated with unvested stock-based compensation awards that have voting rights.

The following table summarizes the activity that occurred during the three months ended March 31, 2011, for each type of share-based incentive award issued by Pioneer:


	Restricted Stock Equity Awards			Restricted Stock Liability Awards			Performance Units		Stock Options			Pioneer Southwest LTIP Restricted Units		Pioneer Southwest LTIP Phantom Units

Outstanding at December 31, 2010		2,559,779			215,134			263,729		507,539			12,212		35,118
Awards granted		404,002			182,982			43,495		86,903			—		30,039
Awards vested		(954,070	)		(63,232	)		—		—			—		—
Options exercised		—			—			—		(14,290	)		—		—
Awards forfeited		(16,011	)		(4,718	)		—		—			—		—

Outstanding at March 31, 2011		1,993,700			330,166			307,224		580,152			12,212		65,157

New accounting pronouncements. During December 2010, the FASB issued ASU No. 2010-28, "Intangibles-Goodwill and Other (Topic 350)." ASU No. 2010-28 modifies step one of the goodwill impairment test for reporting units with zero or negative carrying amounts, requiring that an entity perform step two of the goodwill impairment test if it is more likely than not that a goodwill impairment exists for those reporting units. The Company adopted the provisions of ASU No. 2010-28 effective January 1, 2011. The adoption of ASU No. 2010-28 has no effect on the Company's goodwill balance or the financial position, results of operations or liquidity. See "Goodwill" above for more information about the Company's policy for assessing impairment of its goodwill.

Exploratory Costs

3 Months Ended

Mar. 31, 2011

Exploratory Costs

Exploratory Costs

NOTE C. Exploratory Costs

The Company capitalizes exploratory well and project costs until a determination is made that the well or project has either found proved reserves or is impaired. The Company's capitalized exploratory well and project costs are presented in proved properties in the consolidated balance sheets. If the exploratory well or project is determined to be impaired, the impaired costs are charged to exploration and abandonments expense.

The following table reflects the Company's capitalized exploratory well and project activity during the three months ended March 31, 2011:


	Three Months Ended March 31, 2011
	(in thousands)

Beginning capitalized exploratory costs	$	96,193
Additions to exploratory costs pending the determination of proved reserves		74,264
Reclassification due to determination of proved reserves		(60,344	)
Disposition of assets sold		(28,938	)
Exploratory well costs charged to exploration expense		(645	)


Ending capitalized exploratory costs	$	80,530

The following table provides an aging, as of March 31, 2011 and December 31, 2010 of capitalized exploratory costs and the number of projects for which exploratory costs have been capitalized for a period greater than one year, based on the date drilling was completed:


	March 31, 2011		December 31, 2010
	(in thousands, except project counts)
Capitalized exploratory costs that have been suspended:
One year or less	$	80,530	$	70,635
More than one year		—		25,558


	$	80,530	$	96,193


Number of projects with exploratory costs that have been suspended for a period greater than one year		—		3

Disclosures About Fair Value Measurements

3 Months Ended

Mar. 31, 2011

Disclosures About Fair Value Measurements

Disclosures About Fair Value Measurements

NOTE D. Disclosures About Fair Value Measurements

In accordance with GAAP, fair value measurements are based upon inputs that market participants use in pricing an asset or liability, which are classified into two categories: observable inputs and unobservable inputs. Observable inputs represent market data obtained from independent sources, whereas unobservable inputs reflect a company's own market assumptions, which are used if observable inputs are not reasonably available without undue cost and effort. These two types of inputs are further prioritized into the following fair value input hierarchy:

•

Level 1 – quoted prices for identical assets or liabilities in active markets.

•

Level 2 – quoted prices for similar assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the asset or liability (e.g., interest rates) and inputs derived principally from or corroborated by observable market data by correlation or other means.

•

Level 3 – unobservable inputs for the asset or liability.

The fair value input hierarchy level to which an asset or liability measurement in its entirety falls is determined based on the lowest level input that is significant to the measurement in its entirety.

The following table presents the Company's assets and liabilities that are measured at fair value on a recurring basis as of March 31, 2011, for each of the fair value hierarchy levels:


	Fair Value Measurements at Reporting Date Using
	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Fair Value at March 31, 2011
	(in thousands)

Assets:
Trading securities	$	319	$	25,118	$	—	$	25,437
Commodity derivatives		—		241,894		—		241,894
Interest rate derivatives		—		11,959		—		11,959
Deferred compensation plan assets		39,582		—		—		39,582

Total assets	$	39,901	$	278,971	$	—	$	318,872


Liabilities:
Commodity derivatives	$	—	$	335,279	$	16,675	$	351,954
Interest rate derivatives		—		1,588		—		1,588
Pioneer Southwest credit facility		—		81,289		—		81,289
5.875% senior notes due 2016		482,663		—		—		482,663
6.65% senior notes due 2017		523,908		—		—		523,908
6.875% senior notes due 2018		481,415		—		—		481,415
7.50% senior notes due 2020		507,374		—		—		507,374
7.20% senior notes due 2028		250,000		—		—		250,000
2.875% senior convertible notes due 2038 (a)		854,400		—		—		854,400

Total liabilities	$	3,099,760	$	418,156	$	16,675	$	3,534,591

(a)	The fair value of the 2.875% senior convertible notes includes the fair value of the conversion privilege.

The following table presents the changes in the fair values of the Company's natural gas liquid ("NGL") derivative liabilities classified as Level 3 in the fair value hierarchy:


Fair Value Measurements Using Significant Unobservable Inputs (Level 3)	Three Months Ended March 31, 2011
	(in thousands)
Beginning liability balance	$	(9,556	)
Total gains and losses:
Net unrealized losses included in earnings (a)		(7,118	)
Net realized losses included in earnings (a)		(2,696	)
Settlement payments		2,695

Ending liability balance	$	(16,675	)

(a)	Non-hedge derivatives gains and losses are included in net derivative gains (losses) in the accompanying consolidated statements of operations.

The following table presents the carrying amounts and fair values of the Company's financial instruments as of March 31, 2011 and December 31, 2010:


	March 31, 2011				December 31, 2010
	Carrying Value		Fair Value		Carrying Value		Fair Value
	(in thousands)

Assets:
Commodity price derivatives	$	241,894	$	241,894	$	304,434	$	304,434
Interest rate derivatives	$	11,959	$	11,959	$	18,256	$	18,256
Trading securities	$	25,437	$	25,437	$	467	$	467
Deferred compensation plan assets	$	39,582	$	39,582	$	36,162	$	36,162

Liabilities:
Commodity price derivatives	$	351,954	$	351,954	$	136,867	$	136,867
Interest rate derivatives	$	1,588	$	1,588	$	704	$	704
Pioneer credit facility	$	—	$	—	$	49,000	$	58,382
Pioneer Southwest credit facility	$	85,000	$	81,289	$	81,200	$	77,241
5.875 % senior notes due 2016	$	398,936	$	482,663	$	396,880	$	475,194
6.65 % senior notes due 2017	$	484,079	$	523,908	$	484,045	$	516,632
6.875 % senior notes due 2018	$	449,200	$	481,415	$	449,192	$	480,969
7.50 % senior notes due 2020	$	446,502	$	507,374	$	446,433	$	494,145
7.20 % senior notes due 2028	$	249,926	$	250,000	$	249,925	$	259,350
2.875% senior convertible notes due 2038 (a)	$	449,045	$	854,400	$	444,994	$	728,400

(a)	The fair value of the 2.875% senior convertible notes includes the fair value of the conversion privilege.

Trading securities and deferred compensation plan assets. The Company's trading securities represent securities that are both actively traded and not actively traded on major exchanges. The Company's deferred compensation plan assets represent investments in equity and mutual fund securities that are actively traded on major exchanges plus unallocated contributions as of the measurement date. As of March 31, 2011, all significant inputs to these asset exchange values represented Level 1 independent active exchange market price inputs except inputs for certain trading securities that are not actively traded on major exchanges, which were provided by broker quotes representing Level 2 inputs.

Interest rate derivatives. The Company's interest rate derivative assets and liabilities as of March 31, 2011 represent swap contracts for $470 million notional amount of debt, whereby the Company pays a variable LIBOR-based rate and the counterparty pays a fixed rate of interest. The net derivative values attributable to the Company's interest rate derivative contracts as of March 31, 2011 are based on (i) the contracted notional amounts, (ii) LIBOR rate yield curves provided by counterparties and corroborated with forward active market-quoted LIBOR rate yield curves and (iii) the applicable credit-adjusted risk-free rate yield curve. The Company's interest rate derivative asset and liability measurements represent Level 2 inputs in the hierarchy priority.

Commodity derivatives. The Company's commodity derivatives represent oil, NGL and gas swap contracts, collar contracts and collar contracts with short puts (which are also known as three-way collar contracts). The Company's oil and gas swap, collar and three-way collar derivative contract asset and liability measurements represent Level 2 inputs in the hierarchy priority and NGL derivative contract asset and liability measurements represent Level 3 inputs in the hierarchy priority.

Oil derivatives. The Company's oil derivatives are swap, collar and three-way collar contracts for notional barrels ("Bbls") of oil at fixed (in the case of swap contracts) or interval (in the case of collar and three-way collar contracts) New York Mercantile Exchange ("NYMEX") West Texas Intermediate ("WTI") oil prices. The asset and liability values attributable to the Company's oil derivatives were determined based on (i) the contracted notional volumes, (ii) independent active NYMEX futures price quotes for WTI oil, (iii) the applicable estimated credit-adjusted risk-free rate yield curve and (iv) the implied rate of volatility inherent in the collar and three-way collar contracts. The implied rates of volatility inherent in the Company's collar contracts were determined based on average volatility factors provided by certain independent brokers who are active in buying and selling oil options and were corroborated by market-quoted volatility factors.

NGL derivatives. The Company's NGL derivatives include swap and collar contracts for notional blended Bbls of Mont Belvieu-posted-price NGLs, Conway-posted-price NGLs or NGL component prices per Bbl. The asset and liability values attributable to the Company's NGL derivatives were determined based on (i) the contracted notional volumes, (ii) independent active market-quoted NGL component prices and (iii) the applicable credit-adjusted risk-free rate yield curve. The implied rates of volatility inherent in the Company's collar contracts were determined based on average volatility factors provided by certain independent brokers who are active in buying and selling NGL options and were corroborated by market-quoted volatility factors.

Gas derivatives. The Company's gas derivatives are swap, collar and three-way collar contracts for notional volumes of gas (expressed in millions of British thermal units "MMBtus") contracted at various posted price indexes, including NYMEX Henry Hub ("HH") swap contracts coupled with basis swap contracts that convert the HH price index point to other price indexes. The asset and liability values attributable to the Company's gas derivative contracts were determined based on (i) the contracted notional volumes, (ii) independent active NYMEX futures price quotes for HH gas, (iii) independent market-quoted forward index prices, (iv) the applicable credit-adjusted risk-free rate yield curve and (v) the implied rate of volatility inherent in the collar and three-way collar contracts. The implied rates of volatility inherent in the Company's collar contracts and three-way collar contracts were determined based on average volatility factors provided by certain independent brokers who are active in buying and selling gas options and were corroborated by market-quoted volatility factors.

Credit facility. The fair value of the Company's credit facility and Pioneer Southwest's credit facility is based on (i) forecasted contractual interest and fee payments, (ii) forward active market-quoted LIBOR rate yield curves and (iii) the applicable credit-adjusted risk-free rate yield curve.

Senior notes. The Company's senior notes represent debt securities that are actively traded on major exchanges. The fair values of the Company's senior notes are based on their periodic values as quoted on the major exchanges.

- Definition

This element represents the disclosure related to the fair value measurement of assets and liabilities which includes [financial] instruments measured at fair value that are classified in stockholders' equity. Such assets and liabilities may be measured on a recurring or nonrecurring basis. The disclosures which may be required or desired include: (1) for assets and liabilities measured on a recurring basis, disclosure may include: (a) the fair value measurements at the reporting date; (b) the level within the fair value hierarchy in which the fair value measurements in their entirety fall, segregating fair value measurements using quoted prices in active markets for identical assets or liabilities (Level 1), significant other observable inputs (Level 2), and significant unobservable inputs (Level 3); (c) for fair value measurements using significant unobservable inputs (Level 3), a reconciliation of the beginning and ending balances, separately presenting changes during the period attributable to the following: (i) total gains or losses for the period (realized and unrealized), segregating those gains or losses included in earnings (or changes in net assets), and a description of where those gains or losses included in earnings (or changes in net assets) are reported in the statement of income (or activities); (ii) purchases, sales, issuances, and settlements (net); (iii) transfers in and transfers out of Level 3 (for example, transfers due to changes in the observability of significant inputs); (d) the amount of the total gains or losses for the period in subparagraph (c) (i) above included in earnings (or changes in net assets) that are attributable to the change in unrealized gains or losses relating to those assets and liabilities still held at the reporting date and a description of where those unrealized gains or losses are reported in the statement of income (or activities); (e) the valuation technique(s) used to measure fair value and a discussion of changes in valuation techniques, if any, during the period and (2) for assets and liabilities that are measured at fair value on a nonrecurring basis (for example, impaired assets) disclosure may include, in addition to (a) above: (a) the reasons for the fair value measurements recorded; (b) the same as (b) above; (c) for fair value measurements using significant unobservable inputs (Level 3), a description of the inputs and the information used to develop the inputs; and (d) the valuation technique(s) used to measure fair value and a discussion of changes, if any, in the valuation technique(s) used to measure similar assets and/or liabilities in prior periods.

+ References+ Details

Income Taxes

3 Months Ended

Mar. 31, 2011

Income Taxes

Income Taxes

NOTE E. Income Taxes

The Company accounts for income taxes in accordance with the provisions of ASC Topic 740, which requires that the Company continually assess both positive and negative evidence to determine whether it is more likely than not that deferred tax assets can be realized prior to their expiration. Pioneer monitors Company-specific, oil and gas industry and worldwide economic factors to assess the likelihood that the Company's net operating loss carry forwards ("NOLs") and other deferred tax attributes in the U.S., state, local and foreign tax jurisdictions will be utilized prior to their expiration. As of March 31, 2011 and December 31, 2010, the Company's valuation allowances were $6.6 million and $33.1 million, respectively. The valuation allowance as of December 31, 2010 includes $26.5 million related to Tunisia operations that was classified as discontinued operations held for sale.

ASC 740 also clarifies the accounting for uncertainty in income taxes recognized and prescribes a recognition threshold and measurement methodology for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. As of March 31, 2011, the Company had no significant unrecognized tax benefits. The Company's policy is to account for interest charges with respect to income taxes as interest expense and any penalties, with respect to income taxes, as other expense in the consolidated statements of operations. The Company files income tax returns in the U.S. federal and various state and foreign jurisdictions. With few exceptions, the Company believes that it is no longer subject to examinations by tax authorities for years before 2005. As of March 31, 2011, no adjustments had been proposed in any jurisdiction that would have a significant effect on the Company's liquidity, future results of operations or financial position.

Income tax (provisions) benefits. The Company's income tax (provisions) benefits attributable to income from continuing operations consisted of the following for the three months ended March 31, 2011 and 2010:


	Three Months Ended March 31,
	2011			2010
	(in thousands)

Current:
U.S. federal	$	—		$	(1,101	)
U.S. state		(2,398	)		(1,324	)
Foreign		(6,319	)		(37	)

		(8,717	)		(2,462	)


Deferred:
U.S. federal		40,787			(131,128	)
U.S. state		10,425			(9,460	)
Foreign		4,656			(957	)

		55,868			(141,545	)

Income tax (provision) benefit	$	47,151		$	(144,007	)

Discontinued operations. The Company's income tax (provisions) benefits attributable to income from discontinued operations consisted of the following for the three months ended March 31, 2011 and 2010:


	Three Months Ended March 31,
	2011			2010
	(in thousands)

Current:
U.S. state	$	(5,725	)	$	—
Foreign		(1,849	)		444

		(7,574	)		444


Deferred:
U.S. federal		(227,321	)		70
U.S. state		(2,148	)		—
Foreign		(12,323	)		(16,981	)

		(241,792	)		(16,911	)

Income tax provision	$	(249,366	)	$	(16,467	)

Long-term Debt	3 Months Ended
Long-term Debt	Mar. 31, 2011
Long-term Debt
Long-term Debt	NOTE F. Long-term Debt *Credit Facility.* During March 2011, the Company entered into a Second Amended and Restated 5-Year Revolving Credit Agreement (the "Credit Facility") with a syndicate of financial institutions that matures in March 2016, unless extended in accordance with the terms of the Credit Facility. The Credit Facility replaces the Company's Amended and Restated 5-Year Revolving Credit Agreement entered into in April 2007 (the "Expired Credit Facility") and provides for aggregate loan commitments of $1.25 billion. As of March 31, 2011, the Company had no outstanding borrowings under the Credit Facility and $65.1 million of undrawn letters of credit, all of which were commitments under the Credit Facility, leaving the Company with $1.2 billion of unused borrowing capacity under the Credit Facility. Borrowings under the Credit Facility may be in the form of revolving loans or swing line loans. Aggregate outstanding swing line loans may not exceed $150 million. Revolving loans under the Credit Facility bear interest, at the option of the Company, based on (a) a rate per annum equal to the higher of the prime rate announced from time to time by Wells Fargo Bank, National Association or the weighted average of the rates on overnight Federal funds transactions with members of the Federal Reserve System during the last preceding business day plus 0.5 percent plus a defined alternate base rate spread margin ("ABR Margin"), which is currently one percent based on the Company's debt rating or (b) a base Eurodollar rate, substantially equal to LIBOR, plus a margin (the "Applicable Margin"), which is currently two percent and is also determined by the Company's debt rating. Swing line loans under the Credit Facility bear interest at a rate per annum equal to the "ASK" rate for Federal funds periodically published by the Dow Jones Market Service plus the Applicable Margin. Letters of credit outstanding under the Credit Facility are subject to a per annum fee, representing the Applicable Margin plus 0.125 percent. The Company also pays commitment fees on undrawn amounts under the Credit Facility that are determined by the Company's debt rating (currently 0.375 percent). The Credit Facility contains certain financial covenants, which include the maintenance of a ratio of total debt to book capitalization less intangible assets, accumulated other comprehensive income and certain noncash asset impairments not to exceed .60 to 1.0. The covenants also include the maintenance of a ratio of the net present value of the Company's oil and gas properties to total debt of at least 1.75 to 1.0 until the Company achieves an investment grade rating by Moody's Investors Service, Inc. or Standard & Poors Ratings Group, Inc. As of March 31, 2011, the Company and Pioneer Southwest were in compliance with all of their debt covenants. In accordance with GAAP, the Company accounted for the entry into the Credit Facility as an extinguishment of the Expired Credit Facility. Associated therewith, the Company recorded a $2.4 million loss on extinguishment of debt to write off the unamortized issuance costs of the Company's expired credit facility, which is included in other expense in the accompanying consolidated statement of operations for the three months ended March 31, 2011 (see Note P). *Convertible senior notes.* As of March 31, 2011 and December 31, 2010, the Company had $480 million of 2.875% Convertible Senior Notes outstanding. The 2.875% Convertible Senior Notes are convertible under certain circumstances, using a net share settlement process, into a combination of cash and the Company's common stock pursuant to a formula. Effective April 1, 2011, the Company's 2.875% Convertible Senior Notes became convertible at the option of the holders for the quarter ended June 30, 2011, and may become convertible in future quarters depending on the Company's stock price or other conditions. If the 2.875% Convertible Senior Notes had qualified for and been converted as of March 31, 2011, the note holders would have received $480.0 million of cash and approximately 2.9 million shares of the Company's common stock, which was valued at $295.4 million at March 31, 2011.

Derivative Financial Instruments

3 Months Ended

Mar. 31, 2011

Derivative Financial Instruments

Derivative Financial Instruments

NOTE G. Derivative Financial Instruments

The Company utilizes commodity derivatives contracts to (i) reduce the effect of price volatility on the commodities the Company produces and sells, (ii) support the Company's annual capital budgeting and expenditure plans and (iii) reduce commodity price risk associated with certain capital projects. The Company also, from time to time, utilizes interest rate contracts to reduce the effect of interest rate volatility on the Company's indebtedness and forward currency exchange rate agreements to reduce the effect of exchange rate volatility.

Oil prices. All material physical sales contracts governing the Company's oil production are tied directly or indirectly to NYMEX WTI.

The following table sets forth the volumes in Bbls outstanding as of March 31, 2011 under the Company's oil derivative contracts and the weighted average oil prices per Bbl for those contracts:


	First Quarter		Second Quarter		Third Quarter		Fourth Quarter		Outstanding Average
Average daily oil production associated with derivatives (Bbls):
2011 – Swap contracts
Volume				750		750		750		750
NYMEX price			$	77.25	$	77.25	$	77.25	$	77.25

2011 – Collar contracts
Volume				2,000		2,000		2,000		2,000
NYMEX price:
Ceiling			$	170.00	$	170.00	$	170.00	$	170.00
Floor			$	115.00	$	115.00	$	115.00	$	115.00

2011 – Collar contracts with short puts
Volume				32,000		32,000		32,000		32,000
NYMEX price:
Ceiling			$	99.33	$	99.33	$	99.33	$	99.33
Floor			$	73.75	$	73.75	$	73.75	$	73.75
Short put			$	59.31	$	59.31	$	59.31	$	59.31

2012 – Swap contracts
Volume		3,000		3,000		3,000		3,000		3,000
NYMEX price	$	79.32	$	79.32	$	79.32	$	79.32	$	79.32

2012 – Collar contracts with short puts
Volume		37,000		37,000		37,000		37,000		37,000
NYMEX price:
Ceiling	$	118.34	$	118.34	$	118.34	$	118.34	$	118.34
Floor	$	80.41	$	80.41	$	80.41	$	80.41	$	80.41
Short put	$	65.00	$	65.00	$	65.00	$	65.00	$	65.00

2013 – Swap contracts
Volume		3,000		3,000		3,000		3,000		3,000
NYMEX price	$	81.02	$	81.02	$	81.02	$	81.02	$	81.02

2013 – Collar contracts with short puts
Volume		21,250		21,250		21,250		21,250		21,250
NYMEX price:
Ceiling	$	117.38	$	117.38	$	117.38	$	117.38	$	117.38
Floor	$	80.18	$	80.18	$	80.18	$	80.18	$	80.18
Short put	$	65.18	$	65.18	$	65.18	$	65.18	$	65.18

2014 – Collar contracts with short puts
Volume		12,000		12,000		12,000		12,000		12,000
NYMEX price:
Ceiling	$	128.16	$	128.16	$	128.16	$	128.16	$	128.16
Floor	$	87.92	$	87.92	$	87.92	$	87.92	$	87.92
Short put	$	72.92	$	72.92	$	72.92	$	72.92	$	72.92

Natural gas liquids prices. All material physical sales contracts governing the Company's NGL production are tied directly or indirectly to either Mont Belvieu or Conway fractionation facilities' NGL product component prices.

The following table sets forth the volumes in Bbls outstanding as of March 31, 2011 under the Company's NGL derivative contracts and the weighted average NGL prices per Bbl for those contracts:


	First Quarter		Second Quarter		Third Quarter		Fourth Quarter		Outstanding Average
Average daily NGL production associated with derivatives (Bbls):
2011 – Swap contracts
Volume				1,150		1,150		1,150		1,150
Blended index price			$	51.38	$	51.50	$	51.50	$	51.46

2011 – Collar contracts
Volume				2,650		2,650		2,650		2,650
Index price:
Ceiling			$	64.23	$	64.23	$	64.23	$	64.23
Floor			$	53.29	$	53.29	$	53.29	$	53.29

2012 – Swap contracts
Volume		750		750		750		750		750
Index price	$	35.03	$	35.03	$	35.03	$	35.03	$	35.03

Gas prices. All material physical sales contracts governing the Company's gas production are tied directly or indirectly to regional index prices where the gas is sold. The Company uses derivative contracts to manage gas price volatility and reduce basis risk between NYMEX Henry Hub prices and actual index prices upon which the gas is sold. The following table sets forth the volumes in MMBtus outstanding as of March 31, 2011 under the Company's gas derivative contracts and the weighted average gas prices per MMBtu for those contracts:


	First Quarter			Second Quarter			Third Quarter			Fourth Quarter			Outstanding Average
Average daily gas production associated with derivatives (MMBtus):
2011 – Swap contracts
Volume					117,500			117,500			117,500			117,500
NYMEX price				$	6.13		$	6.13		$	6.13		$	6.13

2011 – Collar contracts with short puts
Volume					200,000			200,000			200,000			200,000
NYMEX price:
Ceiling				$	8.55		$	8.55		$	8.55		$	8.55
Floor				$	6.32		$	6.32		$	6.32		$	6.32
Short put				$	4.88		$	4.88		$	4.88		$	4.88

2011 – Basis swap contracts
Volume					153,500			143,500			143,500			146,809
Price differential				$	(0.53	)	$	(0.56	)	$	(0.56	)	$	(0.55	)

2012 – Swap contracts
Volume		105,000			105,000			105,000			105,000			105,000
NYMEX price	$	5.82		$	5.82		$	5.82		$	5.82		$	5.82

2012 – Collar contracts
Volume		65,000			65,000			65,000			65,000			65,000
NYMEX price:
Ceiling	$	6.60		$	6.60		$	6.60		$	6.60		$	6.60
Floor	$	5.00		$	5.00		$	5.00		$	5.00		$	5.00

2012 – Collar contracts with short puts
Volume		190,000			190,000			190,000			190,000			190,000
NYMEX price:
Ceiling	$	7.96		$	7.96		$	7.96		$	7.96		$	7.96
Floor	$	6.12		$	6.12		$	6.12		$	6.12		$	6.12
Short put	$	4.55		$	4.55		$	4.55		$	4.55		$	4.55
2012 – Basis swap contracts
Volume		116,000			116,000			116,000			116,000			116,000
Price differential	$	(0.37	)	$	(0.37	)	$	(0.37	)	$	(0.37	)	$	(0.37	)

2013 – Swap contracts
Volume		67,500			67,500			67,500			67,500			67,500
NYMEX price	$	6.11		$	6.11		$	6.11		$	6.11		$	6.11

2013 – Collar contracts
Volume		150,000			150,000			150,000			150,000			150,000
NYMEX price:
Ceiling	$	6.25		$	6.25		$	6.25		$	6.25		$	6.25
Floor	$	5.00		$	5.00		$	5.00		$	5.00		$	5.00

2013 – Collar contracts with short puts
Volume		45,000			45,000			45,000			45,000			45,000
NYMEX price:
Ceiling	$	7.49		$	7.49		$	7.49		$	7.49		$	7.49
Floor	$	6.00		$	6.00		$	6.00		$	6.00		$	6.00
Short put	$	4.50		$	4.50		$	4.50		$	4.50		$	4.50

2013 – Basis swap contracts
Volume		32,500			32,500			32,500			32,500			32,500
Price differential	$	(0.34	)	$	(0.34	)	$	(0.34	)	$	(0.34	)	$	(0.34	)

2014 – Swap contracts
Volume		50,000			50,000			50,000			50,000			50,000
NYMEX price	$	6.05		$	6.05		$	6.05		$	6.05		$	6.05

2014 – Collar contracts
Volume		140,000			140,000			140,000			140,000			140,000
NYMEX price:
Ceiling	$	6.44		$	6.44		$	6.44		$	6.44		$	6.44
Floor	$	5.00		$	5.00		$	5.00		$	5.00		$	5.00

2014 – Collar contracts with short puts
Volume		50,000			50,000			50,000			50,000			50,000
NYMEX price:
Ceiling	$	8.08		$	8.08		$	8.08		$	8.08		$	8.08
Floor	$	6.00		$	6.00		$	6.00		$	6.00		$	6.00
Short put	$	4.50		$	4.50		$	4.50		$	4.50		$	4.50

2014 – Basis swap contracts
Volume		10,000			10,000			10,000			10,000			10,000
Price differential	$	(0.16	)	$	(0.16	)	$	(0.16	)	$	(0.16	)	$	(0.16	)

2015 – Collar contracts
Volume		50,000			50,000			50,000			50,000			50,000
NYMEX price:
Ceiling	$	7.92		$	7.92		$	7.92		$	7.92		$	7.92
Floor	$	5.00		$	5.00		$	5.00		$	5.00		$	5.00

Interest rates. The following table sets forth as of March 31, 2011 the notional amount of the Company's debt under outstanding fixed-for-variable interest rate swap contracts, the weighted average fixed annual interest rate and termination date for those contracts:

Type

Notional
Amount

Weighted
Average Fixed
Interest Rate

Termination
Date

(in thousands)

Fixed-for-variable

400,000

2.87 percent

July 2016

Fixed-for-variable

70,000

3.23 percent

March 2017

Tabular disclosure of derivative financial instruments. All of the Company's derivatives are accounted for as non-hedge derivatives as of March 31, 2011 and December 31, 2010. The following tables provide disclosure of the Company's derivative instruments:

Fair Value of Derivative Instruments as of March 31, 2011

Asset Derivatives (a)

Liability Derivatives (a)

Type

Balance Sheet
Location

Fair
Value

Balance Sheet
Location

Fair
Value

(in thousands)

Derivatives not designated as hedging instruments

Commodity price derivatives

Derivatives - current

145,952

Derivatives - current

183,747

Interest rate derivatives

Derivatives - current

11,810

Derivatives - current

—

Commodity price derivatives

Derivatives - noncurrent

118,591

Derivatives - noncurrent

190,856

Interest rate derivatives

Derivatives - noncurrent

9,306

Derivatives - noncurrent

10,745

Total derivatives not designated as hedging instruments

285,659

385,348

Total derivatives

285,659

385,348

Fair Value of Derivative Instruments as of December 31, 2010

Asset Derivatives (a)

Liability Derivatives (a)

Type

Balance Sheet
Location

Fair
Value

Balance Sheet
Location

Fair
Value

(in thousands)

Derivatives not designated as hedging instruments

Commodity price derivatives

Derivatives - current

167,406

Derivatives - current

87,741

Interest rate derivatives

Derivatives - current

11,903

Derivatives - current

886

Commodity price derivatives

Derivatives - noncurrent

152,731

Derivatives - noncurrent

64,829

Interest rate derivatives

Derivatives - noncurrent

15,762

Derivatives - noncurrent

9,227

Total derivatives not designated as hedging instruments

347,802

162,683

Total derivatives

347,802

162,683

(a)	Derivative assets and liabilities shown in the tables above are presented as gross assets and liabilities, without regard to master netting arrangements which are considered in the presentations of derivative assets and liabilities in the accompanying consolidated balance sheets.


Derivatives in Cash Flow Hedging Relationships	Location of Gain/(Loss) Reclassified from AOCI into Earnings		Amount of Gain/(Loss) Reclassified from AOCI into Earnings
			Three Months Ended March 31,
			2011			2010
			(in thousands)

Interest rate derivatives		Interest expense	$	(68	)	$	(1,058	)
Interest rate derivatives		Derivative gains (losses), net		—			(1,142	)
Commodity price derivatives		Oil and gas revenue		8,124			23,126

Total			$	8,056		$	20,926


Derivatives Not Designated as Hedging Instruments	Location of Gain (Loss) Recognized in Earnings on Derivatives		Amount of Gain (Loss) Recognized in Earnings on Derivatives
			Three Months Ended March 31,
			2011			2010
			(in thousands)

Interest rate derivatives		Derivative gains (losses), net	$	(2,152	)	$	11,399
Commodity price derivatives		Derivative gains (losses), net		(242,280	)		255,219

Total			$	(244,432	)	$	266,618

AOCI - Hedging. As of March 31, 2011 and December 31, 2010, AOCI - Hedging represented net deferred gains of $3.4 million and $7.4 million, respectively. The AOCI - Hedging balance as of March 31, 2011 was comprised of $21.6 million of net deferred gains on the effective portions of discontinued commodity hedges, $1.9 million of net deferred losses on the effective portions of discontinued interest rate hedges and $5.9 million of associated net deferred tax provisions, reduced by $10.4 million of AOCI – Hedging net deferred gains attributable to and classified as noncontrolling interests in consolidated subsidiaries.

During the twelve months ending March 31, 2012, the Company expects to reclassify $24.0 million of AOCI – Hedging net deferred gains to oil revenues (including $10.4 million related to noncontrolling interests) and $291 thousand of AOCI – Hedging net deferred losses to interest expense. The Company also expects to reclassify $8.5 million of net deferred income tax provisions associated with hedge derivatives during the twelve months ending March 31, 2012 from AOCI - Hedging to income tax expense. For the remaining nine months of 2011, the Company expects to reclassify deferred gains on discontinued commodity hedges of $24.8 million to oil revenues. During 2012, the Company expects to reclassify deferred losses on commodity hedges of $3.2 million to oil revenues. The aforementioned $1.9 million of net deferred hedge losses on the effective portion of interest rate hedges will be transferred from AOCI-Hedging to interest expense ratably through April 2018.

Asset Retirement Obligations

3 Months Ended

Mar. 31, 2011

Asset Retirement Obligations

Asset Retirement Obligations

NOTE H. Asset Retirement Obligations

The Company's asset retirement obligations primarily relate to the future plugging and abandonment of wells and related facilities. Market risk premiums associated with asset retirement obligations are estimated to represent a component of the Company's credit-adjusted risk-free rate that is utilized in the calculations of asset retirement obligations. The following table summarizes the Company's asset retirement obligation activity during the three months ended March 31, 2011 and 2010:


	Three Months Ended March 31,
	2011			2010
	(in thousands)

Beginning asset retirement obligations	$	152,291		$	166,434
Liabilities assumed in acquisitions		6			—
New wells placed on production		671			278
Changes in estimates		300			—
Disposition of wells		(81	)		(26,248	)
Liabilities settled		(1,234	)		(1,154	)
Accretion of discount from continuing operations		2,655			2,859
Accretion of discount from discontinued operations		81			101


Ending asset retirement obligations	$	154,689		$	142,270

The Company records the current and noncurrent portions of asset retirement obligations in other current liabilities and other liabilities, respectively, in the accompanying consolidated balance sheets. As of March 31, 2011 and December 31, 2010, the current portions of the Company's asset retirement obligations were $19.4 million and $19.9 million, respectively.

Postretirement Benefit Obligations

3 Months Ended

Mar. 31, 2011

Postretirement Benefit Obligations

Postretirement Benefit Obligations

NOTE I. Postretirement Benefit Obligations

As of March 31, 2011 and December 31, 2010, the Company had $7.2 million and $7.4 million, respectively, of unfunded accumulated postretirement benefit obligations, the current and noncurrent portions of which are included in other current liabilities and other liabilities in the accompanying consolidated balance sheets. These obligations are comprised of five plans of which four relate to predecessor entities that the Company acquired in prior years. These plans had no assets as of March 31, 2011 or December 31, 2010. Other than participants in the Company's retirement plan, the participants of these plans are not current employees of the Company.

The following table reconciles changes in the Company's unfunded accumulated postretirement benefit obligations during the three months ended March 31, 2011 and March 31, 2010:


	Three Months Ended March 31,
	2011			2010
	(in thousands)

Beginning accumulated postretirement benefit obligations	$	7,408		$	9,075
Net benefit payments		(316	)		(312	)
Service costs		61			80
Accretion of interest		78			108


Ending accumulated postretirement benefit obligations	$	7,231		$	8,951

- Definition

Description containing the entire pension and other postretirement benefits disclosure as a single block of text.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 158

-Paragraph 7, 21, 22

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5, 6, 7, 8

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 8

-Subparagraph m

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 106

-Paragraph 518

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 87

-Paragraph 264

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph b

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph a

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph h

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph q

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name FASB Staff Position (FSP)

-Number FAS106-2

-Paragraph 20, 21, 22

Reference 11: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Emerging Issues Task Force (EITF)

-Number 03-2

-Paragraph 8

Reference 12: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 30

-Paragraph 26

Reference 13: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Implementation Guide (Q and A)

-Number FAS88

-Paragraph 63

+ Details

Commitments and Contingencies	3 Months Ended
Commitments and Contingencies	Mar. 31, 2011
Commitments and Contingencies
Commitments and Contingencies	NOTE J. Commitments and Contingencies *Legal actions.* In addition to the legal action described below, the Company is a party to other proceedings and claims incidental to its business. While many of these matters involve inherent uncertainty, the Company believes that the amount of the liability, if any, ultimately incurred with respect to such other proceedings and claims will not have a material adverse effect on the Company's consolidated financial position as a whole or on its liquidity, capital resources or future annual results of operations. The Company will continue to evaluate its litigation on a quarter-by-quarter basis and will establish and adjust any litigation reserves as appropriate to reflect its assessment of the then current status of litigation. Investigation by the Alaska Oil and Gas Conservation Commission (the "AOGCC"). During the second quarter of 2010, the AOGCC commenced an investigation into allegations by a former Pioneer employee regarding the Company's Oooguruk facility on the North Slope of Alaska. Among the allegations are claims that the Company did not have authorization to inject certain non-hazardous substances into its enhanced oil recovery well, that the Company mishandled disposal of waste products and that the Company's operating practices are harmful to the project's oil reservoirs. Upon initially becoming aware of the allegations, the Company informed the AOGCC and other relevant federal, state and local agencies and commenced its own investigation, which confirmed injections of non-hazardous fluids into the Oooguruk enhanced oil recovery well without prior authorizations to do so. The results of the Company's investigation were reported to the agencies. In December 2010, the AOGCC investigator submitted a report outlining its findings, which (i) found that the Company's operating practices have not harmed the project's oil reservoirs and (ii) raised certain regulatory compliance issues, all of which the Company previously reported or has since taken actions to remedy. Although the Company does not know at this time what action the AOGCC will take in response to the report, based on the facts as known to date, the Company believes that compliance with any order or other action of the AOGCC will not materially and negatively affect the Company's liquidity, financial position or future results of operations. *Obligations following divestitures.* In April 2006, the Company provided the purchaser of its Argentine assets certain indemnifications. The Company remains responsible for certain contingent liabilities related to such indemnifications, subject to defined limitations, including matters of litigation, environmental contingencies, royalty obligations and income taxes. The Company has also retained certain liabilities and indemnified buyers for certain matters in connection with other divestitures, including the sale in 2007 of its Canadian assets and the February 2011 sale of Pioneer Tunisia. The Company does not believe that these obligations are probable of having a material impact on its liquidity, financial position or future results of operations.

Net Income (Loss) Per Share

3 Months Ended

Mar. 31, 2011

Net Income (Loss) Per Share

Net Income (Loss) Per Share

NOTE K. Net Income (Loss) Per Share

In accordance with GAAP, the Company uses the two-class method of calculating net income (loss) per share because certain of the Company's and its consolidated subsidiaries' unvested share-based awards qualify as participating securities. Participating securities participate in the Company's dividend distributions and are assumed to participate in the Company's undistributed income proportionate to weighted average outstanding common shares, but are not assumed to participate in the Company's net losses because they are not contractually obligated to do so. Accordingly, allocations of earnings to participating securities are included in the Company's calculations of basic and diluted earnings per share from continuing operations, discontinued operations and total net income attributable to common stockholders.

During periods in which the Company realizes a loss from continuing operations attributable to common stockholders, such as during the three months ended March 31, 2011, securities or other contracts to issue common stock would be dilutive to loss per share from continuing operations; therefore, conversion into common stock is assumed not to occur.

The following tables reconcile the Company's net income (loss) from continuing operations, discontinued operations and total net income attributable to common stockholders to the basic and diluted earnings used in the two-class method to determine the Company's net income (loss) per share amounts for the three months ended March 31, 2011 and 2010:


	Three Months Ended March 31, 2011
	Continuing Operations			Discontinued Operations			Total
	(in thousands)

Income (loss) as reported	$	(70,838	)	$	414,642		$	348,594
Net loss attributable to the noncontrolling interests		4,790			—			—
Participating basic earnings		—			(6,140	)		(6,140	)

Basic income (loss) attributable to common stockholders		(66,048	)		408,502			342,454
Diluted adjustments to earnings		—			—			—

Diluted income (loss) attributable to common stockholders	$	(66,048	)	$	408,502		$	342,454


	Three Months Ended March 31, 2010
	Continuing Operations			Discontinued Operations			Total
	(in thousands)

Income as reported	$	256,795		$	3,811		$	245,254
Net income attributable to the noncontrolling interests		(15,352	)		—			—
Participating basic earnings		(5,254	)		(83	)		(5,337	)

Basic income attributable to common stockholders		236,189			3,728			239,917
Diluted adjustments to earnings		50			1			51

Diluted income attributable to common stockholders	$	236,239		$	3,729		$	239,968

The following table is a reconciliation of basic weighted average common shares outstanding to diluted weighted average common shares outstanding for the three months ended March 31, 2011 and 2010:


	Three Months Ended March 31,
	2011		2010
	(in thousands)

Weighted average common shares outstanding:
Basic		115,869		114,655
Dilutive common stock options (a)		—		224
Contingently issuable - performance shares (a)		—		583


Diluted		115,869		115,462

(a)

The following common stock equivalents were excluded from the diluted income per share calculation for the three months ended March 31, 2011 because they would have been anti-dilutive to the loss from continuing operations: 198,463 outstanding options to purchase the Company's common stock, 416,703 common shares attributable to unvested performance units and 2,898,761 common shares issuable if holders of the Company's 2.875% Convertible Senior Notes had exercised their conversion rights (see Note F).

Geographic Operating Segment Information

3 Months Ended

Mar. 31, 2011

Geographic Operating Segment Information

Geographic Operating Segment Information

NOTE L. Geographic Operating Segment Information

The Company has reportable operations in only one industry segment, that being the oil and gas exploration and production industry; however, the Company is organizationally structured along geographic operating segments or regions. The Company has reportable continuing operations in the United States and South Africa.

The following tables provide the Company's geographic operating segment data for the three months ended March 31, 2011 and 2010. Geographic operating segment income tax (provisions) benefits have been determined based on statutory rates existing in the various tax jurisdictions where the Company has oil and gas producing activities. The "Headquarters" table column includes income and expenses that are not routinely included in the earnings measures internally reported to management on a geographic operating segment basis.


	United States			South Africa			Headquarters			Consolidated Total
	(in thousands)

Three Months Ended March 31, 2011
Revenues and other income:
Oil and gas	$	475,729		$	21,401		$	—		$	497,130
Interest and other		—			—			32,687			32,687
Loss on disposition of assets, net		—			—			(2,191	)		(2,191	)

		475,729			21,401			30,496			527,626

Costs and expenses:
Oil and gas production		98,835			1,096			—			99,931
Production and ad valorem taxes		33,296			—			—			33,296
Depletion, depreciation and amortization		116,540			13,685			10,148			140,373
Exploration and abandonments		17,485			158			—			17,643
General and administrative		—			—			44,106			44,106
Accretion of discount on asset retirement obligations		2,044			611			—			2,655
Interest		—			—			45,227			45,227
Hurricane activity, net		71			—			—			71
Derivative losses, net		—			—			244,432			244,432
Other		5,159			—			12,722			17,881

		273,430			15,550			356,635			645,615

Income (loss) from continuing operations before income taxes		202,299			5,851			(326,139	)		(117,989	)
Income tax benefit (provision)		(74,851	)		(1,638	)		123,640			47,151

Income (loss) from continuing operations	$	127,448		$	4,213		$	(202,499	)	$	(70,838	)


Three Months Ended March 31, 2010
Revenues and other income:
Oil and gas	$	446,664		$	25,381		$	—		$	472,045
Interest and other		—			—			18,008			18,008
Gain (loss) on disposition of assets, net		17,419			—			(476	)		16,943

		464,083			25,381			17,532			506,996

Costs and expenses:
Oil and gas production		85,324			776			—			86,100
Production and ad valorem taxes		27,061			—			—			27,061
Depletion, depreciation and amortization		115,505			21,897			7,026			144,428
Exploration and abandonments		16,776			72			—			16,848
General and administrative		—			—			38,315			38,315
Accretion of discount on asset retirement obligations		2,237			622			—			2,859
Interest		—			—			47,523			47,523
Hurricane activity, net		(7,410	)		—			—			(7,410	)
Derivative gains, net		—			—			(265,476	)		(265,476	)
Other		10,281			—			5,665			15,946

		249,774			23,367			(166,947	)		106,194

Income from continuing operations before income taxes		214,309			2,014			184,479			400,802
Income tax provision		(79,294	)		(564	)		(64,149	)		(144,007	)

Income from continuing operations	$	135,015		$	1,450		$	120,330		$	256,795


	March 31, 2011		December 31, 2010
	(in thousands)
Consolidating Assets by Geographic Area:
United States	$	9,818,634	$	8,987,141
South Africa		111,703		134,901
Tunisia		—		325,942
Headquarters		95,649		231,118

Total consolidated assets	$	10,025,986	$	9,679,102

Volumetric Production Payments

3 Months Ended

Mar. 31, 2011

Volumetric Production Payments

Volumetric Production Payments

NOTE M. Volumetric Production Payments

The Company's remaining VPP represents a limited-term overriding royalty interest in oil reserves that: (i) entitles the purchaser to receive production volumes over a period of time from specific lease interests, (ii) is free and clear of all associated future production costs and capital expenditures associated with the reserves, (iii) is nonrecourse to the Company (i.e., the purchaser's only recourse is to the reserves acquired), (iv) transfer title of the reserves to the purchaser and (v) allow the Company to retain the remaining reserves after the VPP's volumetric quantities have been delivered.

At the inception of the VPP agreement, the Company (i) removed the proved reserves associated with the VPP, (ii) recognized VPP proceeds as deferred revenue which are being amortized on a unit-of-production basis to oil revenues over the remaining term of the VPP, (iii) retained responsibility for 100 percent of the production costs and capital costs related to VPP interests and (iv) no longer recognizes production associated with the VPP volumes.

The following table provides information about changes in the deferred revenue carrying values of the Company's VPP for the three months ended March 31, 2011 (in thousands):


Deferred revenue at December 31, 2010	$	87,020
Less: 2011 amortization		(11,083	)

Deferred revenue at March 31, 2011	$	75,937

The remaining deferred revenue amounts will be recognized in oil revenues in the consolidated statements of operations as noted below, assuming the related VPP production volumes are delivered as scheduled (in thousands):


Remaining 2011	$	33,866
2012		42,071

	$	75,937

Gain (Loss) on Disposition of Assets, Net

3 Months Ended

Mar. 31, 2011

Gain (Loss) on Disposition of Assets, Net

Gain (Loss) on Disposition of Assets, Net

NOTE N.

Gain (Loss) on Disposition of Assets, Net

For the three months ended March 31, 2011, the Company recorded $2.2 million of net losses on disposition of from continuing operations as compared to $16.9 million of net gains from continuing operations for the three months ended March 31, 2010.

The Company's $2.2 million net loss during the three months ended March 31, 2011 was primarily associated with sales of excess materials and supplies inventory. During the three months ended March 31, 2010, the Company's net gain was primarily associated with certain proved and unproved oil and gas properties divested in the Uinta/Piceance area.

See Note Q for information about the Company's gain during the three months ended March 31, 2011 from the sale of its Tunisia subsidiaries, representing discontinued operations.

Interest and Other Income

3 Months Ended

Mar. 31, 2011

Interest and Other Income

Interest and Other Income

NOTE O. Interest and Other Income

The following table provides the components of the Company's interest and other income:


	Three Months Ended March 31,
	2011		2010
	(in thousands)

Alaskan Petroleum Production Tax credits (a)	$	27,452	$	14,248
Drilling and servicing margin		2,878		510
Deferred compensation plan income		867		510
Other income		1,002		691
Equity interest in income of unconsolidated affiliate		298		—
Interest income		190		384
Insurance claim recovery		—		1,665

Total interest and other income	$	32,687	$	18,008

(a)	The Company earns Alaskan Petroleum Production Tax ("PPT") credits on qualifying capital expenditures. The Company recognizes income from PPT credits when they are realized through cash refunds or sales.

Other Expense

3 Months Ended

Mar. 31, 2011

Other Expense

Other Expense

NOTE P. Other Expense

The following table provides the components of the Company's other expense:


	Three Months Ended March 31,
	2011		2010
	(in thousands)

Transportation commitment charge (a)	$	5,272	$	—
Excess and terminated rig related costs (b)		5,159		10,281
Other		2,494		650
Loss on extinguishment of debt		2,367		—
Contingency and environmental accrual adjustments		1,295		153
Cancelled well costs		991		—
Inventory impairment (c)		285		1,557
Bad debt expense		18		224
Well servicing operations (d)		—		3,081

Total other expense	$	17,881	$	15,946

(a)	Primarily represents firm transportation contract deficiency payment obligations.

(b)	Represents above market drilling rig costs, idle rig costs and costs incurred to terminate contractual drilling rig commitments prior to their contractual maturities.

(c)	Represents impairment charges on excess materials and supplies inventories.

(d)	Represents idle well servicing costs.

Discontinued Operations

3 Months Ended

Mar. 31, 2011

Discontinued Operations

Discontinued Operations

NOTE Q. Discontinued Operations

During December 2010, the Company committed to a plan to sell Pioneer Tunisia and in February 2011 completed the sale of 100 percent of the Company's share holdings in Pioneer Tunisia to an unaffiliated party for net cash proceeds of $845.2 million, resulting in a pretax gain of $649.9 million. Accordingly, the historical results of operations of Pioneer Tunisia have been classified as discontinued operations herein. The net cash proceeds from the sale of Pioneer Tunisia were determined in accordance with the sale and purchase agreement that the Company entered into with the purchaser, which provides for certain customary adjustments for matters occurring after the effective date of the sale, such as capital contributions and distributions, and working capital adjustments. Adjustments to net cash proceeds involve management's best estimate about the realizable value of working capital items, including that the amounts are reasonably assured of collection. Differences between actual working capital amounts and management's estimates recorded as of March 31, 2011, if any, will be recorded as income or loss from discontinued operations in future periods.

The following table represents the components of the Company's discontinued operations for the three months ended March 31, 2011 and 2010:


	Three Months Ended March 31,
	2011			2010
	(in thousands)

Revenues and other income:
Oil and gas	$	22,130		$	35,752
Interest and other (a)		4,568			1,795
Gain on disposition of assets, net		649,872			—

		676,570			37,547

Costs and expenses:
Oil and gas production		2,126			3,616
Depletion, depreciation and amortization (b)		—			6,340
Exploration and abandonments		2,554			3,950
General and administrative		6,619			2,633
Accretion of discount on asset retirement obligations (b)		81			101
Other		1,182			629

		12,562			17,269

Income from discontinued operations before income taxes		664,008			20,278
Current tax (provision) benefit		(7,574	)		444
Deferred tax provision (b)		(241,792	)		(16,911	)

Income from discontinued operations	$	414,642		$	3,811

(a)	Includes $2.0 million of interest received during the first quarter of 2011 from the Bureau of Ocean Energy Management, Regulation, and Enforcement related to the recovery of excess royalties paid by the Company on qualifying deepwater leases in the Gulf of Mexico.

(b)	Represents the significant noncash components of discontinued operations.

Subsequent Events	3 Months Ended
Subsequent Events	Mar. 31, 2011
Subsequent Events
Subsequent Events	NOTE R. Subsequent Events The Company has evaluated subsequent events through the date of issuance of its unaudited consolidated financial statements. Except as disclosed in Note F, the Company is not aware of any reportable subsequent events.

Basis of Presentation (Policy)

3 Months Ended

Mar. 31, 2011

Basis of Presentation

Presentation

Discontinued Operations

Allowances for Doubtful Accounts


	Three Months Ended March 31, 2011
	(in thousands)

Beginning allowance for doubtful accounts balance	$	3,674
Amount recorded in other expense for bad debt expense		18
Other net decreases		(157	)


Ending allowance for doubtful accounts balance	$	3,535

Inventories

Derivatives and Hedging

Goodwill

Noncontrolling Interest in Consolidated Subsidiaries

Investment in Unconsolidated Affiliate

Stock-based Compensation

The following table summarizes the activity that occurred during the three months ended March 31, 2011, for each type of share-based incentive award issued by Pioneer:


	Restricted Stock Equity Awards			Restricted Stock Liability Awards			Performance Units		Stock Options			Pioneer Southwest LTIP Restricted Units		Pioneer Southwest LTIP Phantom Units

Outstanding at December 31, 2010		2,559,779			215,134			263,729		507,539			12,212		35,118
Awards granted		404,002			182,982			43,495		86,903			—		30,039
Awards vested		(954,070	)		(63,232	)		—		—			—		—
Options exercised		—			—			—		(14,290	)		—		—
Awards forfeited		(16,011	)		(4,718	)		—		—			—		—

Outstanding at March 31, 2011		1,993,700			330,166			307,224		580,152			12,212		65,157

New Accounting Pronouncements

Basis of Presentation (Tables)

3 Months Ended

Mar. 31, 2011

Basis of Presentation

Allowance for Doubtful Accounts


	Three Months Ended March 31, 2011
	(in thousands)

Beginning allowance for doubtful accounts balance	$	3,674
Amount recorded in other expense for bad debt expense		18
Other net decreases		(157	)


Ending allowance for doubtful accounts balance	$	3,535

Stock-based Awards, Lapses, Exercises and Forfeitures


	Restricted Stock Equity Awards			Restricted Stock Liability Awards			Performance Units		Stock Options			Pioneer Southwest LTIP Restricted Units		Pioneer Southwest LTIP Phantom Units

Outstanding at December 31, 2010		2,559,779			215,134			263,729		507,539			12,212		35,118
Awards granted		404,002			182,982			43,495		86,903			—		30,039
Awards vested		(954,070	)		(63,232	)		—		—			—		—
Options exercised		—			—			—		(14,290	)		—		—
Awards forfeited		(16,011	)		(4,718	)		—		—			—		—

Outstanding at March 31, 2011		1,993,700			330,166			307,224		580,152			12,212		65,157

Exploratory Costs (Tables)

3 Months Ended

Mar. 31, 2011

Exploratory Costs

Capitalized Exploratory Well and Project Activity


	Three Months Ended March 31, 2011
	(in thousands)

Beginning capitalized exploratory costs	$	96,193
Additions to exploratory costs pending the determination of proved reserves		74,264
Reclassification due to determination of proved reserves		(60,344	)
Disposition of assets sold		(28,938	)
Exploratory well costs charged to exploration expense		(645	)


Ending capitalized exploratory costs	$	80,530

Capitalized Exploratory Costs and the Number of Projects for Which Exploratory Costs have been Capitalized


	March 31, 2011		December 31, 2010
	(in thousands, except project counts)
Capitalized exploratory costs that have been suspended:
One year or less	$	80,530	$	70,635
More than one year		—		25,558


	$	80,530	$	96,193


Number of projects with exploratory costs that have been suspended for a period greater than one year		—		3

Disclosures About Fair Value Measurements (Tables)

3 Months Ended

Mar. 31, 2011

Disclosures About Fair Value Measurements

Assets and Liabilities that are Measured at Fair Value on a Recurring Basis


	Fair Value Measurements at Reporting Date Using
	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Fair Value at March 31, 2011
	(in thousands)

Assets:
Trading securities	$	319	$	25,118	$	—	$	25,437
Commodity derivatives		—		241,894		—		241,894
Interest rate derivatives		—		11,959		—		11,959
Deferred compensation plan assets		39,582		—		—		39,582

Total assets	$	39,901	$	278,971	$	—	$	318,872


Liabilities:
Commodity derivatives	$	—	$	335,279	$	16,675	$	351,954
Interest rate derivatives		—		1,588		—		1,588
Pioneer Southwest credit facility		—		81,289		—		81,289
5.875% senior notes due 2016		482,663		—		—		482,663
6.65% senior notes due 2017		523,908		—		—		523,908
6.875% senior notes due 2018		481,415		—		—		481,415
7.50% senior notes due 2020		507,374		—		—		507,374
7.20% senior notes due 2028		250,000		—		—		250,000
2.875% senior convertible notes due 2038 (a)		854,400		—		—		854,400

Total liabilities	$	3,099,760	$	418,156	$	16,675	$	3,534,591

(a)	The fair value of the 2.875% senior convertible notes includes the fair value of the conversion privilege.

Fair Value Measurements Using Significant Unobservable Inputs


Fair Value Measurements Using Significant Unobservable Inputs (Level 3)	Three Months Ended March 31, 2011
	(in thousands)
Beginning liability balance	$	(9,556	)
Total gains and losses:
Net unrealized losses included in earnings (a)		(7,118	)
Net realized losses included in earnings (a)		(2,696	)
Settlement payments		2,695

Ending liability balance	$	(16,675	)

(a)	Non-hedge derivatives gains and losses are included in net derivative gains (losses) in the accompanying consolidated statements of operations.

Fair Values of the Company Financial Instruments


	March 31, 2011				December 31, 2010
	Carrying Value		Fair Value		Carrying Value		Fair Value
	(in thousands)

Assets:
Commodity price derivatives	$	241,894	$	241,894	$	304,434	$	304,434
Interest rate derivatives	$	11,959	$	11,959	$	18,256	$	18,256
Trading securities	$	25,437	$	25,437	$	467	$	467
Deferred compensation plan assets	$	39,582	$	39,582	$	36,162	$	36,162

Liabilities:
Commodity price derivatives	$	351,954	$	351,954	$	136,867	$	136,867
Interest rate derivatives	$	1,588	$	1,588	$	704	$	704
Pioneer credit facility	$	—	$	—	$	49,000	$	58,382
Pioneer Southwest credit facility	$	85,000	$	81,289	$	81,200	$	77,241
5.875 % senior notes due 2016	$	398,936	$	482,663	$	396,880	$	475,194
6.65 % senior notes due 2017	$	484,079	$	523,908	$	484,045	$	516,632
6.875 % senior notes due 2018	$	449,200	$	481,415	$	449,192	$	480,969
7.50 % senior notes due 2020	$	446,502	$	507,374	$	446,433	$	494,145
7.20 % senior notes due 2028	$	249,926	$	250,000	$	249,925	$	259,350
2.875% senior convertible notes due 2038 (a)	$	449,045	$	854,400	$	444,994	$	728,400

(a)	The fair value of the 2.875% senior convertible notes includes the fair value of the conversion privilege.

Income Taxes (Tables)

3 Months Ended

Mar. 31, 2011

Income Taxes

Income Tax (Provisions) Benefits


	Three Months Ended March 31,
	2011			2010
	(in thousands)

Current:
U.S. federal	$	—		$	(1,101	)
U.S. state		(2,398	)		(1,324	)
Foreign		(6,319	)		(37	)

		(8,717	)		(2,462	)


Deferred:
U.S. federal		40,787			(131,128	)
U.S. state		10,425			(9,460	)
Foreign		4,656			(957	)

		55,868			(141,545	)

Income tax (provision) benefit	$	47,151		$	(144,007	)

Discontinued Operations


	Three Months Ended March 31,
	2011			2010
	(in thousands)

Current:
U.S. state	$	(5,725	)	$	—
Foreign		(1,849	)		444

		(7,574	)		444


Deferred:
U.S. federal		(227,321	)		70
U.S. state		(2,148	)		—
Foreign		(12,323	)		(16,981	)

		(241,792	)		(16,911	)

Income tax provision	$	(249,366	)	$	(16,467	)

Derivative Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2011

Derivative Financial Instruments

Oil Derivative Contracts Volume and Weighted Average Price


	First Quarter		Second Quarter		Third Quarter		Fourth Quarter		Outstanding Average
Average daily oil production associated with derivatives (Bbls):
2011 – Swap contracts
Volume				750		750		750		750
NYMEX price			$	77.25	$	77.25	$	77.25	$	77.25

2011 – Collar contracts
Volume				2,000		2,000		2,000		2,000
NYMEX price:
Ceiling			$	170.00	$	170.00	$	170.00	$	170.00
Floor			$	115.00	$	115.00	$	115.00	$	115.00

2011 – Collar contracts with short puts
Volume				32,000		32,000		32,000		32,000
NYMEX price:
Ceiling			$	99.33	$	99.33	$	99.33	$	99.33
Floor			$	73.75	$	73.75	$	73.75	$	73.75
Short put			$	59.31	$	59.31	$	59.31	$	59.31

2012 – Swap contracts
Volume		3,000		3,000		3,000		3,000		3,000
NYMEX price	$	79.32	$	79.32	$	79.32	$	79.32	$	79.32

2012 – Collar contracts with short puts
Volume		37,000		37,000		37,000		37,000		37,000
NYMEX price:
Ceiling	$	118.34	$	118.34	$	118.34	$	118.34	$	118.34
Floor	$	80.41	$	80.41	$	80.41	$	80.41	$	80.41
Short put	$	65.00	$	65.00	$	65.00	$	65.00	$	65.00

2013 – Swap contracts
Volume		3,000		3,000		3,000		3,000		3,000
NYMEX price	$	81.02	$	81.02	$	81.02	$	81.02	$	81.02

2013 – Collar contracts with short puts
Volume		21,250		21,250		21,250		21,250		21,250
NYMEX price:
Ceiling	$	117.38	$	117.38	$	117.38	$	117.38	$	117.38
Floor	$	80.18	$	80.18	$	80.18	$	80.18	$	80.18
Short put	$	65.18	$	65.18	$	65.18	$	65.18	$	65.18

2014 – Collar contracts with short puts
Volume		12,000		12,000		12,000		12,000		12,000
NYMEX price:
Ceiling	$	128.16	$	128.16	$	128.16	$	128.16	$	128.16
Floor	$	87.92	$	87.92	$	87.92	$	87.92	$	87.92
Short put	$	72.92	$	72.92	$	72.92	$	72.92	$	72.92

Natural Gas Liquids Volume and Weighted Average Price


	First Quarter		Second Quarter		Third Quarter		Fourth Quarter		Outstanding Average
Average daily NGL production associated with derivatives (Bbls):
2011 – Swap contracts
Volume				1,150		1,150		1,150		1,150
Blended index price			$	51.38	$	51.50	$	51.50	$	51.46

2011 – Collar contracts
Volume				2,650		2,650		2,650		2,650
Index price:
Ceiling			$	64.23	$	64.23	$	64.23	$	64.23
Floor			$	53.29	$	53.29	$	53.29	$	53.29

2012 – Swap contracts
Volume		750		750		750		750		750
Index price	$	35.03	$	35.03	$	35.03	$	35.03	$	35.03

Gas Volume and Weighted Average Price

	First Quarter			Second Quarter			Third Quarter			Fourth Quarter			Outstanding Average
Average daily gas production associated with derivatives (MMBtus):
2011 – Swap contracts
Volume					117,500			117,500			117,500			117,500
NYMEX price				$	6.13		$	6.13		$	6.13		$	6.13
2011 – Collar contracts with short puts
Volume					200,000			200,000			200,000			200,000
NYMEX price:
Ceiling				$	8.55		$	8.55		$	8.55		$	8.55
Floor				$	6.32		$	6.32		$	6.32		$	6.32
Short put				$	4.88		$	4.88		$	4.88		$	4.88
2011 – Basis swap contracts
Volume					153,500			143,500			143,500			146,809
Price differential				$	(0.53	)	$	(0.56	)	$	(0.56	)	$	(0.55	)
2012 – Swap contracts
Volume		105,000			105,000			105,000			105,000			105,000
NYMEX price	$	5.82		$	5.82		$	5.82		$	5.82		$	5.82
2012 – Collar contracts
Volume		65,000			65,000			65,000			65,000			65,000
NYMEX price:
Ceiling	$	6.60		$	6.60		$	6.60		$	6.60		$	6.60
Floor	$	5.00		$	5.00		$	5.00		$	5.00		$	5.00
2012 – Collar contracts with short puts
Volume		190,000			190,000			190,000			190,000			190,000
NYMEX price:
Ceiling	$	7.96		$	7.96		$	7.96		$	7.96		$	7.96
Floor	$	6.12		$	6.12		$	6.12		$	6.12		$	6.12
Short put	$	4.55		$	4.55		$	4.55		$	4.55		$	4.55
2012 – Basis swap contracts
Volume		116,000			116,000			116,000			116,000			116,000
Price differential	$	(0.37	)	$	(0.37	)	$	(0.37	)	$	(0.37	)	$	(0.37	)
2013 – Swap contracts
Volume		67,500			67,500			67,500			67,500			67,500
NYMEX price	$	6.11		$	6.11		$	6.11		$	6.11		$	6.11
2013 – Collar contracts
Volume		150,000			150,000			150,000			150,000			150,000
NYMEX price:
Ceiling	$	6.25		$	6.25		$	6.25		$	6.25		$	6.25
Floor	$	5.00		$	5.00		$	5.00		$	5.00		$	5.00
2013 – Collar contracts with short puts
Volume		45,000			45,000			45,000			45,000			45,000
NYMEX price:
Ceiling	$	7.49		$	7.49		$	7.49		$	7.49		$	7.49
Floor	$	6.00		$	6.00		$	6.00		$	6.00		$	6.00
Short put	$	4.50		$	4.50		$	4.50		$	4.50		$	4.50
2013 – Basis swap contracts
Volume		32,500			32,500			32,500			32,500			32,500
Price differential	$	(0.34	)	$	(0.34	)	$	(0.34	)	$	(0.34	)	$	(0.34	)
2014 – Swap contracts
Volume		50,000			50,000			50,000			50,000			50,000
NYMEX price	$	6.05		$	6.05		$	6.05		$	6.05		$	6.05
2014 – Collar contracts
Volume		140,000			140,000			140,000			140,000			140,000
NYMEX price:
Ceiling	$	6.44		$	6.44		$	6.44		$	6.44		$	6.44
Floor	$	5.00		$	5.00		$	5.00		$	5.00		$	5.00
2014 – Collar contracts with short puts
Volume		50,000			50,000			50,000			50,000			50,000
NYMEX price:
Ceiling	$	8.08		$	8.08		$	8.08		$	8.08		$	8.08
Floor	$	6.00		$	6.00		$	6.00		$	6.00		$	6.00
Short put	$	4.50		$	4.50		$	4.50		$	4.50		$	4.50
2014 – Basis swap contracts
Volume		10,000			10,000			10,000			10,000			10,000
Price differential	$	(0.16	)	$	(0.16	)	$	(0.16	)	$	(0.16	)	$	(0.16	)
2015 – Collar contracts
Volume		50,000			50,000			50,000			50,000			50,000
NYMEX price:
Ceiling	$	7.92		$	7.92		$	7.92		$	7.92		$	7.92
Floor	$	5.00		$	5.00		$	5.00		$	5.00		$	5.00

Fixed-for-Variable Interest Rates

Type

Notional
Amount

Weighted
Average Fixed
Interest Rate

Termination
Date

(in thousands)

Fixed-for-variable

400,000

2.87 percent

July 2016

Fixed-for-variable

70,000

3.23 percent

March 2017

Derivative Instrument

Fair Value of Derivative Instruments as of March 31, 2011

Asset Derivatives (a)

Liability Derivatives (a)

Type

Balance Sheet
Location

Fair
Value

Balance Sheet
Location

Fair
Value

(in thousands)

Derivatives not designated as hedging instruments

Commodity price derivatives

Derivatives - current

145,952

Derivatives - current

183,747

Interest rate derivatives

Derivatives - current

11,810

Derivatives - current

—

Commodity price derivatives

Derivatives - noncurrent

118,591

Derivatives - noncurrent

190,856

Interest rate derivatives

Derivatives - noncurrent

9,306

Derivatives - noncurrent

10,745

Total derivatives not designated as hedging instruments

285,659

385,348

Total derivatives

285,659

385,348

Fair Value of Derivative Instruments as of December 31, 2010

Asset Derivatives (a)

Liability Derivatives (a)

Type

Balance Sheet
Location

Fair
Value

Balance Sheet
Location

Fair
Value

(in thousands)

Derivatives not designated as hedging instruments

Commodity price derivatives

Derivatives - current

167,406

Derivatives - current

87,741

Interest rate derivatives

Derivatives - current

11,903

Derivatives - current

886

Commodity price derivatives

Derivatives - noncurrent

152,731

Derivatives - noncurrent

64,829

Interest rate derivatives

Derivatives - noncurrent

15,762

Derivatives - noncurrent

9,227

Total derivatives not designated as hedging instruments

347,802

162,683

Total derivatives

347,802

162,683

(a)	Derivative assets and liabilities shown in the tables above are presented as gross assets and liabilities, without regard to master netting arrangements which are considered in the presentations of derivative assets and liabilities in the accompanying consolidated balance sheets.

Derivative Obligations under Terminated Hedge Arrangements


Derivatives in Cash Flow Hedging Relationships	Location of Gain/(Loss) Reclassified from AOCI into Earnings		Amount of Gain/(Loss) Reclassified from AOCI into Earnings
			Three Months Ended March 31,
			2011			2010
			(in thousands)

Interest rate derivatives		Interest expense	$	(68	)	$	(1,058	)
Interest rate derivatives		Derivative gains (losses), net		—			(1,142	)
Commodity price derivatives		Oil and gas revenue		8,124			23,126

Total			$	8,056		$	20,926


Derivatives Not Designated as Hedging Instruments	Location of Gain (Loss) Recognized in Earnings on Derivatives		Amount of Gain (Loss) Recognized in Earnings on Derivatives
			Three Months Ended March 31,
			2011			2010
			(in thousands)

Interest rate derivatives		Derivative gains (losses), net	$	(2,152	)	$	11,399
Commodity price derivatives		Derivative gains (losses), net		(242,280	)		255,219

Total			$	(244,432	)	$	266,618

Asset Retirement Obligations (Tables)

3 Months Ended

Mar. 31, 2011

Asset Retirement Obligations

Asset Retirement Obligations


	Three Months Ended March 31,
	2011			2010
	(in thousands)

Beginning asset retirement obligations	$	152,291		$	166,434
Liabilities assumed in acquisitions		6			—
New wells placed on production		671			278
Changes in estimates		300			—
Disposition of wells		(81	)		(26,248	)
Liabilities settled		(1,234	)		(1,154	)
Accretion of discount from continuing operations		2,655			2,859
Accretion of discount from discontinued operations		81			101


Ending asset retirement obligations	$	154,689		$	142,270

Postretirement Benefit Obligations (Tables)

3 Months Ended

Mar. 31, 2011

Postretirement Benefit Obligations

Accumulated Postretirement Benefit Obligations


	Three Months Ended March 31,
	2011			2010
	(in thousands)

Beginning accumulated postretirement benefit obligations	$	7,408		$	9,075
Net benefit payments		(316	)		(312	)
Service costs		61			80
Accretion of interest		78			108


Ending accumulated postretirement benefit obligations	$	7,231		$	8,951

Net Income (Loss) Per Share (Tables)

3 Months Ended

Mar. 31, 2011

Net Income (Loss) Per Share

Reconciliation of Earnings Attributable to Common Stockholders, Basic and Diluted


	Three Months Ended March 31, 2011
	Continuing Operations			Discontinued Operations			Total
	(in thousands)

Income (loss) as reported	$	(70,838	)	$	414,642		$	348,594
Net loss attributable to the noncontrolling interests		4,790			—			—
Participating basic earnings		—			(6,140	)		(6,140	)

Basic income (loss) attributable to common stockholders		(66,048	)		408,502			342,454
Diluted adjustments to earnings		—			—			—

Diluted income (loss) attributable to common stockholders	$	(66,048	)	$	408,502		$	342,454


	Three Months Ended March 31, 2010
	Continuing Operations			Discontinued Operations			Total
	(in thousands)

Income as reported	$	256,795		$	3,811		$	245,254
Net income attributable to the noncontrolling interests		(15,352	)		—			—
Participating basic earnings		(5,254	)		(83	)		(5,337	)

Basic income attributable to common stockholders		236,189			3,728			239,917
Diluted adjustments to earnings		50			1			51

Diluted income attributable to common stockholders	$	236,239		$	3,729		$	239,968

Reconciliation of Basic Weighted Average Common Shares


	Three Months Ended March 31,
	2011		2010
	(in thousands)

Weighted average common shares outstanding:
Basic		115,869		114,655
Dilutive common stock options (a)		—		224
Contingently issuable - performance shares (a)		—		583


Diluted		115,869		115,462

(a)

Geographic Operating Segment Information (Tables)

3 Months Ended

Mar. 31, 2011

Geographic Operating Segment Information

Schedule of Income Statement by Geographic Operating Segment


	United States			South Africa			Headquarters			Consolidated Total
	(in thousands)

Three Months Ended March 31, 2011
Revenues and other income:
Oil and gas	$	475,729		$	21,401		$	—		$	497,130
Interest and other		—			—			32,687			32,687
Loss on disposition of assets, net		—			—			(2,191	)		(2,191	)

		475,729			21,401			30,496			527,626

Costs and expenses:
Oil and gas production		98,835			1,096			—			99,931
Production and ad valorem taxes		33,296			—			—			33,296
Depletion, depreciation and amortization		116,540			13,685			10,148			140,373
Exploration and abandonments		17,485			158			—			17,643
General and administrative		—			—			44,106			44,106
Accretion of discount on asset retirement obligations		2,044			611			—			2,655
Interest		—			—			45,227			45,227
Hurricane activity, net		71			—			—			71
Derivative losses, net		—			—			244,432			244,432
Other		5,159			—			12,722			17,881

		273,430			15,550			356,635			645,615

Income (loss) from continuing operations before income taxes		202,299			5,851			(326,139	)		(117,989	)
Income tax benefit (provision)		(74,851	)		(1,638	)		123,640			47,151

Income (loss) from continuing operations	$	127,448		$	4,213		$	(202,499	)	$	(70,838	)


Three Months Ended March 31, 2010
Revenues and other income:
Oil and gas	$	446,664		$	25,381		$	—		$	472,045
Interest and other		—			—			18,008			18,008
Gain (loss) on disposition of assets, net		17,419			—			(476	)		16,943

		464,083			25,381			17,532			506,996

Costs and expenses:
Oil and gas production		85,324			776			—			86,100
Production and ad valorem taxes		27,061			—			—			27,061
Depletion, depreciation and amortization		115,505			21,897			7,026			144,428
Exploration and abandonments		16,776			72			—			16,848
General and administrative		—			—			38,315			38,315
Accretion of discount on asset retirement obligations		2,237			622			—			2,859
Interest		—			—			47,523			47,523
Hurricane activity, net		(7,410	)		—			—			(7,410	)
Derivative gains, net		—			—			(265,476	)		(265,476	)
Other		10,281			—			5,665			15,946

		249,774			23,367			(166,947	)		106,194

Income from continuing operations before income taxes		214,309			2,014			184,479			400,802
Income tax provision		(79,294	)		(564	)		(64,149	)		(144,007	)

Income from continuing operations	$	135,015		$	1,450		$	120,330		$	256,795

Reconciliation of Assets from Segment to Consolidated


	March 31, 2011		December 31, 2010
	(in thousands)
Consolidating Assets by Geographic Area:
United States	$	9,818,634	$	8,987,141
South Africa		111,703		134,901
Tunisia		—		325,942
Headquarters		95,649		231,118

Total consolidated assets	$	10,025,986	$	9,679,102

Volumetric Production Payments (Tables)

3 Months Ended

Mar. 31, 2011

Volumetric Production Payments

Deferred Revenue Carrying Values


Deferred revenue at December 31, 2010	$	87,020
Less: 2011 amortization		(11,083	)

Deferred revenue at March 31, 2011	$	75,937

Revenue Recognition in Future Periods


Remaining 2011	$	33,866
2012		42,071

	$	75,937

Interest and Other Income (Tables)

3 Months Ended

Mar. 31, 2011

Interest and Other Income

Interest and Other Income


	Three Months Ended March 31,
	2011		2010
	(in thousands)

Alaskan Petroleum Production Tax credits (a)	$	27,452	$	14,248
Drilling and servicing margin		2,878		510
Deferred compensation plan income		867		510
Other income		1,002		691
Equity interest in income of unconsolidated affiliate		298		—
Interest income		190		384
Insurance claim recovery		—		1,665

Total interest and other income	$	32,687	$	18,008

(a)	The Company earns Alaskan Petroleum Production Tax ("PPT") credits on qualifying capital expenditures. The Company recognizes income from PPT credits when they are realized through cash refunds or sales.

Other Expense (Tables)

3 Months Ended

Mar. 31, 2011

Other Expense

Schedule of Components of Other Expense


	Three Months Ended March 31,
	2011		2010
	(in thousands)

Transportation commitment charge (a)	$	5,272	$	—
Excess and terminated rig related costs (b)		5,159		10,281
Other		2,494		650
Loss on extinguishment of debt		2,367		—
Contingency and environmental accrual adjustments		1,295		153
Cancelled well costs		991		—
Inventory impairment (c)		285		1,557
Bad debt expense		18		224
Well servicing operations (d)		—		3,081

Total other expense	$	17,881	$	15,946

(a)	Primarily represents firm transportation contract deficiency payment obligations.

(b)	Represents above market drilling rig costs, idle rig costs and costs incurred to terminate contractual drilling rig commitments prior to their contractual maturities.

(c)	Represents impairment charges on excess materials and supplies inventories.

(d)	Represents idle well servicing costs.

Discontinued Operations (Tables)

3 Months Ended

Mar. 31, 2011

Discontinued Operations

Schedule of Discontinued Operations

	Three Months Ended March 31,
	2011			2010
	(in thousands)

Revenues and other income:
Oil and gas	$	22,130		$	35,752
Interest and other (a)		4,568			1,795
Gain on disposition of assets, net		649,872			—

		676,570			37,547

Costs and expenses:
Oil and gas production		2,126			3,616
Depletion, depreciation and amortization (b)		—			6,340
Exploration and abandonments		2,554			3,950
General and administrative		6,619			2,633
Accretion of discount on asset retirement obligations (b)		81			101
Other		1,182			629

		12,562			17,269

Income from discontinued operations before income taxes		664,008			20,278
Current tax (provision) benefit		(7,574	)		444
Deferred tax provision (b)		(241,792	)		(16,911	)

Income from discontinued operations	$	414,642		$	3,811

(a)	Includes $2.0 million of interest received during the first quarter of 2011 from the Bureau of Ocean Energy Management, Regulation, and Enforcement related to the recovery of excess royalties paid by the Company on qualifying deepwater leases in the Gulf of Mexico.

(b)	Represents the significant noncash components of discontinued operations.

Basis of Presentation (Narrative) (Details) (USD $)	3 Months Ended		12 Months Ended
Basis of Presentation (Narrative) (Details) (USD $)	Mar. 31, 2011	Mar. 31, 2010	Dec. 31, 2010
Percentage of divest of subsidiaries capital stock	100.00%
Allowances for doubtful accounts	$ 3,535,000		$ 3,674,000
Materials and supplies inventories	206,800,000		183,400,000
Commodities	3,800,000		3,900,000
Net materials and supplies inventories reserves	3,800,000		3,600,000
Inventory value classified as other noncurrent assets	22,900,000		13,700,000
Basis points added to variable interest rate	250
Noncontrolling interest in net assets subsidiaries	90,900,000		105,400,000
Net income attributable to the noncontrolling interests	(4,790,000)	15,352,000
Allocated stock-based compensation expense	13,000,000	9,800,000
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	three
Restricted stock awards unvested shares at balance sheet date	566,389		825,796
Restricted stock awards liability	28,000,000
Unrecognized compensation expense	109,100,000
Sendero [Member]
Number of operating drilling rigs	14
EFS Midstream [Member]
Percent of interest owned	50.10%
Tunisian Subsidiaries [Member]
Inventories classified as discontinued operations held for sale			13,600,000
Limited Partner Interest [Member] \| Pioneer Southwest [Member]
Partnerships interest of oil and gas	61.90%
General Partner Interest [Member] \| Subsidiaries [Member]
Partnerships interest of oil and gas	0.10%
Restricted Stock Awards [Member]
Amount of liabilities attributable to liability awards included in accounts payable	$ 1,600,000

Basis of Presentation (Allowance for Doubtful Accounts) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2011	Mar. 31, 2010
Basis of Presentation
Beginning allowance for doubtful accounts balance	$ 3,674
Amount recorded in other expense for bad debt expense	18	224
Other net decreases	(157)
Ending allowance for doubtful accounts balance	$ 3,535

Basis of Presentation (Stock-based Awards, Lapses, Exercises and Forfeitures) (Details)	3 Months Ended						3 Months Ended
	Mar. 31, 2011 Restricted Stock Awards [Member]	Mar. 31, 2011 Restricted Stock Liability Awards [Member]	Mar. 31, 2011 Performance Units [Member]	Mar. 31, 2011 Stock Options [Member]	Mar. 31, 2011 Pioneer Southwest LTIP Restricted Units [Member]	Dec. 31, 2010 Pioneer Southwest LTIP Restricted Units [Member]	Mar. 31, 2011 Pioneer Southwest LTIP Phantom Units [Member]
Outstanding at December 31, 2010	2,559,779	215,134	263,729	507,539	12,212	12,212	35,118
Awards granted	404,002	182,982	43,495	86,903			30,039
Awards vested	(954,070)	(63,232)
Options exercised				(14,290)
Awards forfeited	(16,011)	(4,718)
Outstanding at March 31, 2011	1,993,700	330,166	307,224	580,152	12,212	12,212	65,157

Exploratory Costs (Capitalized Exploratory Well and Project Activity) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2011
Exploratory Costs
Beginning capitalized exploratory costs	$ 96,193
Additions to exploratory costs pending the determination of proved reserves	74,264
Reclassification due to determination of proved reserves	(60,344)
Disposition of assets sold	(28,938)
Exploratory well costs charged to exploration expense	(645)
Ending capitalized exploratory costs	$ 80,530

Exploratory Costs (Capitalized Exploratory Costs and the Number of Projects for Which Exploratory Costs have been Capitalized) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2011	Dec. 31, 2010
Exploratory Costs
One year or less	$ 80,530	$ 70,635
More than one year		25,558
Capitalized exploratory costs, total	$ 80,530	$ 96,193
Number of projects with exploratory costs that have been suspended for a period greater than one year		3

Disclosures About Fair Value Measurements (Assets and Liabilities that are Measured at Fair Value on a Recurring Basis) (Details) (USD $)

3 Months Ended

Mar. 31, 2011

Assets, (Fair Value, Total)

$ 318,872,000

Liabilities, (Fair Value, Total)

3,534,591,000

Swap contract notional amount fixed rate of interest and variable LIBOR

470,000,000

5.875% Senior Notes Due 2016 [Member]

Liabilities, (Fair Value, Total)

482,663,000

Senior notes, interest rate

5.875%

Debt instrument expiration date

2016

6.65% Senior Notes Due 2017 [Member]

Liabilities, (Fair Value, Total)

523,908,000

Senior notes, interest rate

6.65%

Debt instrument expiration date

2017

6.875% Senior Notes Due 2018 [Member]

Liabilities, (Fair Value, Total)

481,415,000

Senior notes, interest rate

6.875%

Debt instrument expiration date

2018

7.50% Senior Notes Due 2020 [Member]

Liabilities, (Fair Value, Total)

507,374,000

Senior notes, interest rate

7.50%

Debt instrument expiration date

2020

7.20% Senior Notes Due 2028 [Member]

Liabilities, (Fair Value, Total)

250,000,000

Senior notes, interest rate

7.20%

Debt instrument expiration date

2028

2.875% Convertible Senior Notes Due 2038 [Member]

Liabilities, (Fair Value, Total)

854,400,000

^[1]

Senior notes, interest rate

2.875%

Debt instrument expiration date

2038

Trading Securities [Member]

Assets, (Fair Value, Total)

25,437,000

Commodity Derivatives [Member]

Assets, (Fair Value, Total)

241,894,000

Liabilities, (Fair Value, Total)

351,954,000

Deferred Compensation Plan Assets [Member]

Assets, (Fair Value, Total)

39,582,000

Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]

Assets, (Fair Value, Total)

39,901,000

Liabilities, (Fair Value, Total)

3,099,760,000

Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | 5.875% Senior Notes Due 2016 [Member]

Liabilities, (Fair Value, Total)

482,663,000

Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | 6.65% Senior Notes Due 2017 [Member]

Liabilities, (Fair Value, Total)

523,908,000

Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | 6.875% Senior Notes Due 2018 [Member]

Liabilities, (Fair Value, Total)

481,415,000

Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | 7.50% Senior Notes Due 2020 [Member]

Liabilities, (Fair Value, Total)

507,374,000

Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | 7.20% Senior Notes Due 2028 [Member]

Liabilities, (Fair Value, Total)

250,000,000

Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | 2.875% Convertible Senior Notes Due 2038 [Member]

Liabilities, (Fair Value, Total)

854,400,000

^[1]

Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Trading Securities [Member]

Assets, (Fair Value, Total)

319,000

Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Deferred Compensation Plan Assets [Member]

Assets, (Fair Value, Total)

39,582,000

Significant Other Observable Inputs (Level 2) [Member]

Assets, (Fair Value, Total)

278,971,000

Liabilities, (Fair Value, Total)

418,156,000

Significant Other Observable Inputs (Level 2) [Member] | Trading Securities [Member]

Assets, (Fair Value, Total)

25,118,000

Significant Other Observable Inputs (Level 2) [Member] | Commodity Derivatives [Member]

Assets, (Fair Value, Total)

241,894,000

Liabilities, (Fair Value, Total)

335,279,000

Significant Unobservable Inputs (Level 3) [Member]

Liabilities, (Fair Value, Total)

16,675,000

Significant Unobservable Inputs (Level 3) [Member] | Commodity Derivatives [Member]

Liabilities, (Fair Value, Total)

16,675,000

Pioneer Southwest Credit Facility [Member]

Liabilities, (Fair Value, Total)

81,289,000

Pioneer Southwest Credit Facility [Member] | Significant Other Observable Inputs (Level 2) [Member]

Liabilities, (Fair Value, Total)

81,289,000

Interest Rate Derivatives [Member]

Assets, (Fair Value, Total)

11,959,000

Liabilities, (Fair Value, Total)

1,588,000

Interest Rate Derivatives [Member] | Significant Other Observable Inputs (Level 2) [Member]

Assets, (Fair Value, Total)

11,959,000

Liabilities, (Fair Value, Total)

$ 1,588,000

[1]	The fair value of the 2.875% senior convertible notes includes the fair value of the conversion privilege.

Disclosures About Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) (NGL Swap Contracts [Member], USD $)
In Thousands, unless otherwise specified

3 Months Ended

Mar. 31, 2011

NGL Swap Contracts [Member]

Beginning liability balance

$ (9,556)

Net unrealized losses included in earnings

(7,118)

^[1]

Net realized losses included in earnings

(2,696)

^[1]

Settlement payments

2,695

Ending liability balance

$ (16,675)

[1]	Non-hedge derivatives gains and losses are included in net derivative gains (losses) in the accompanying consolidated statements of operations.

Disclosures About Fair Value Measurements (Fair Values of the Company's Financial Instruments) (Details) (USD $)
In Thousands, unless otherwise specified

3 Months Ended

Mar. 31, 2011

Dec. 31, 2010

5.875% Senior Notes Due 2016 [Member]

Liabilities

Carrying Value

$ 398,936

$ 396,880

Fair Value

482,663

475,194

Senior notes, interest rate

5.875%

Debt instrument expiration date

2016

6.65% Senior Notes Due 2017 [Member]

Liabilities

Carrying Value

484,079

484,045

Fair Value

523,908

516,632

Senior notes, interest rate

6.65%

Debt instrument expiration date

2017

6.875% Senior Notes Due 2018 [Member]

Liabilities

Carrying Value

449,200

449,192

Fair Value

481,415

480,969

Senior notes, interest rate

6.875%

Debt instrument expiration date

2018

7.50% Senior Notes Due 2020 [Member]

Liabilities

Carrying Value

446,502

446,433

Fair Value

507,374

494,145

Senior notes, interest rate

7.50%

Debt instrument expiration date

2020

7.20% Senior Notes Due 2028 [Member]

Liabilities

Carrying Value

249,926

249,925

Fair Value

250,000

259,350

Senior notes, interest rate

7.20%

Debt instrument expiration date

2028

2.875% Convertible Senior Notes Due 2038 [Member]

Liabilities

Carrying Value

449,045

^[1]

444,994

^[1]

Fair Value

854,400

^[1]

728,400

^[1]

Senior notes, interest rate

2.875%

Debt instrument expiration date

2038

Trading Securities [Member]

Assets

Carrying Value

25,437

467

Fair Value

25,437

467

Commodity Derivatives [Member]

Assets

Carrying Value

241,894

304,434

Fair Value

241,894

304,434

Liabilities

Carrying Value

351,954

136,867

Fair Value

351,954

136,867

Deferred Compensation Plan Assets [Member]

Assets

Carrying Value

39,582

36,162

Fair Value

39,582

36,162

Pioneer Southwest Credit Facility [Member]

Liabilities

Carrying Value

85,000

81,200

Fair Value

81,289

77,241

Pioneer Credit Facility [Member]

Liabilities

Carrying Value

49,000

Fair Value

58,382

Interest Rate Derivatives [Member]

Assets

Carrying Value

11,959

18,256

Fair Value

11,959

18,256

Liabilities

Carrying Value

1,588

704

Fair Value

$ 1,588

$ 704

[1]	The fair value of the 2.875% senior convertible notes includes the fair value of the conversion privilege.

Income Taxes (Income Tax (Provisions) Benefits) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2011	Mar. 31, 2010
Income Taxes
U.S. federal		$ (1,101)
U.S. state	(2,398)	(1,324)
Foreign	(6,319)	(37)
Current income tax (provision) benefit	(8,717)	(2,462)
U.S. federal	40,787	(131,128)
U.S. state	10,425	(9,460)
Foreign	4,656	(957)
Deferred income tax (provision) benefit	55,868	(141,545)
Income tax (provision) benefit	$ 47,151	$ (144,007)

Income Taxes (Discontinued Operations) (Details) (USD $)
In Thousands, unless otherwise specified

3 Months Ended

Mar. 31, 2011

Mar. 31, 2010

Income Taxes

U.S. state

$ (5,725)

Foreign

(1,849)

444

Total current tax (provision) benefit

(7,574)

444

U.S. federal

(227,321)

U.S. state

(2,148)

Foreign

(12,323)

(16,981)

Total deferred tax (provision) benefit

(241,792)

^[1]

(16,911)

^[1]

Income tax (provision) benefit

$ (249,366)

$ (16,467)

[1]	Represents the significant noncash components of discontinued operations.

Long-term Debt (Narrative) (Details) (USD $)	3 Months Ended
Long-term Debt (Narrative) (Details) (USD $)	Mar. 31, 2011
Line of credit facility, maximum borrowing capacity	$ 1,250,000,000
Outstanding borrowings under the Credit Facility	0
Undrawn letters of credit	65,100,000
Unused borrowing capacity	1,200,000,000
Aggregate outstanding swing line loans maximum	150,000,000
Credit facility, description	(a) a rate per annum equal to the higher of the prime rate announced from time to time by Wells Fargo Bank, National Association or the weighted average of the rates on overnight Federal funds transactions with members of the Federal Reserve System during the last preceding business day plus 0.5 percent plus a defined alternate base rate spread margin ("ABR Margin"), which is currently one percent based on the Company's debt rating or (b) a base Eurodollar rate, substantially equal to LIBOR, plus a margin (the "Applicable Margin"), which is currently two percent and is also determined by the Company's debt rating. Swing line loans under the Credit Facility bear interest at a rate per annum equal to the "ASK" rate for Federal funds periodically published by the Dow Jones Market Service plus the Applicable Margin. Letters of credit outstanding under the Credit Facility are subject to a per annum fee, representing the Applicable Margin plus 0.125 percent. The Company also pays commitment fees on undrawn amounts under the Credit Facility that are determined by the Company's debt rating (currently 0.375 percent).
Loss on extinguishment of debt to write off the unamortized issuance costs	2,400,000
2.875% Convertible Senior Notes [Member]
Senior notes, interest rate	2.875%
Senior convertible notes, outstanding	480,000,000
Shares received for conversion of debt	2,900,000
Value of shares received for conversion of debt	$ 295,400,000
Total Debt to Book Capitalization [Member]
Debt instrument covenant description	.60 to 1.0
Company's Oil and Gas Properties to Total Debt [Member]
Debt instrument covenant description	1.75 to 1.0

Derivative Financial Instruments (Narrative) (Details) (USD $)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2011	Dec. 31, 2011	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2010
Net deferred gains	$ 3,439,000				$ 7,361,000
Net deferred gains on the effective portions of discontinued commodity hedges	21,600,000
Net deferred losses on the effective portions of discontinued interest rate hedges	1,900,000
Net deferred gains or losses associated to net deferred tax provisions	5,900,000
Net deferred gains or losses attributable to noncontrolling interests	10,400,000
Expected to reclassify accumulated other comprehensive income - Hedging net deferred gains				24,000,000
Accumulated other comprehensive income - Hedging net deferred gains related to noncontrolling interests				10,400,000
Cash flow hedge loss reclassified to interest expense				291,000
Expected to reclassify net deferred income tax provision				8,500,000
Expected to reclassify deferred gains (losses) on discontinued commodity hedges		24,800,000
Expected to reclassify accumulated other comprehensive income - Hedging net deferred losses			3,200,000
Through April 2018 [Member]
Net deferred losses on the effective portions of discontinued interest rate hedges	$ 1,900,000

Derivative Financial Instruments (Oil Derivative Contracts Volume and Weighted Average Price) (Details)	3 Months Ended				12 Months Ended
	Dec. 31, 2011 bbl	Sep. 30, 2011 bbl	Jun. 30, 2011 bbl	Mar. 31, 2011 bbl	Dec. 31, 2011 bbl
2011 - Swap Contracts [Member]
Volume	750,000,000,000	750,000,000,000	750,000,000,000		750,000,000,000
NYMEX price	77.25	77.25	77.25		77.25
2011 - Collar Contracts [Member]
Volume	2,000,000,000,000	2,000,000,000,000	2,000,000,000,000		2,000,000,000,000
2011 - Collar Contracts [Member] \| Ceiling [Member]
NYMEX price	170.00	170.00	170.00		170.00
2011 - Collar Contracts [Member] \| Floor [Member]
NYMEX price	115.00	115.00	115.00		115.00
2011 - Collar Contracts with Short Puts [Member]
Volume	32,000,000,000,000	32,000,000,000,000	32,000,000,000,000		32,000,000,000,000
2011 - Collar Contracts with Short Puts [Member] \| Ceiling [Member]
NYMEX price	99.33	99.33	99.33		99.33
2011 - Collar Contracts with Short Puts [Member] \| Floor [Member]
NYMEX price	73.75	73.75	73.75		73.75
2011 - Collar Contracts with Short Puts [Member] \| Short Put [Member]
NYMEX price	59.31	59.31	59.31		59.31
2012 - Swap Contracts [Member]
Volume	3,000,000,000,000	3,000,000,000,000	3,000,000,000,000	3,000,000,000,000	3,000,000,000,000
NYMEX price	79.32	79.32	79.32	79.32	79.32
2012 - Collar Contracts with Short Puts [Member]
Volume	37,000,000,000,000	37,000,000,000,000	37,000,000,000,000	37,000,000,000,000	37,000,000,000,000
2012 - Collar Contracts with Short Puts [Member] \| Ceiling [Member]
NYMEX price	118.34	118.34	118.34	118.34	118.34
2012 - Collar Contracts with Short Puts [Member] \| Floor [Member]
NYMEX price	80.41	80.41	80.41	80.41	80.41
2012 - Collar Contracts with Short Puts [Member] \| Short Put [Member]
NYMEX price	65.00	65.00	65.00	65.00	65.00
2013 - Swap Contracts [Member]
Volume	3,000,000,000,000	3,000,000,000,000	3,000,000,000,000	3,000,000,000,000	3,000,000,000,000
NYMEX price	81.02	81.02	81.02	81.02	81.02
2013 - Collar Contracts With Short Puts [Member]
Volume	21,250,000,000,000	21,250,000,000,000	21,250,000,000,000	21,250,000,000,000	21,250,000,000,000
2013 - Collar Contracts With Short Puts [Member] \| Ceiling [Member]
NYMEX price	117.38	117.38	117.38	117.38	117.38
2013 - Collar Contracts With Short Puts [Member] \| Floor [Member]
NYMEX price	80.18	80.18	80.18	80.18	80.18
2013 - Collar Contracts With Short Puts [Member] \| Short Put [Member]
NYMEX price	65.18	65.18	65.18	65.18	65.18
2014 - Collar Contracts with Short Puts [Member]
Volume	12,000,000,000,000	12,000,000,000,000	12,000,000,000,000	12,000,000,000,000	12,000,000,000,000
2014 - Collar Contracts with Short Puts [Member] \| Ceiling [Member]
NYMEX price	128.16	128.16	128.16	128.16	128.16
2014 - Collar Contracts with Short Puts [Member] \| Floor [Member]
NYMEX price	87.92	87.92	87.92	87.92	87.92
2014 - Collar Contracts with Short Puts [Member] \| Short Put [Member]
NYMEX price	72.92	72.92	72.92	72.92	72.92

Derivative Financial Instruments (Natural Gas Liquids Volume and Weighted Average Price) (Details)	3 Months Ended				12 Months Ended
	Dec. 31, 2011 bbl	Sep. 30, 2011 bbl	Jun. 30, 2011 bbl	Mar. 31, 2011 bbl	Dec. 31, 2011 bbl
2011 - Swap Contracts [Member]
Volume	1,150	1,150	1,150		1,150
Index price	51.50	51.50	51.38		51.46
2011 - Collar Contracts [Member]
Volume	2,650	2,650	2,650		2,650
2011 - Collar Contracts [Member] \| Ceiling [Member]
Index price	64.23	64.23	64.23		64.23
2011 - Collar Contracts [Member] \| Floor [Member]
Index price	53.29	53.29	53.29		53.29
2012 - Swap Contracts [Member]
Volume	750	750	750	750	750
Index price	35.03	35.03	35.03	35.03	35.03

Derivative Financial Instruments (Gas Volume and Weighted Average Price) (Details)	3 Months Ended				12 Months Ended
	Dec. 31, 2011 Mmbtu	Sep. 30, 2011 Mmbtu	Jun. 30, 2011 Mmbtu	Mar. 31, 2011 Mmbtu	Dec. 31, 2011 Mmbtu
2011 - Swap Contracts [Member]
Volume	117,500	117,500	117,500		117,500
NYMEX price	6.13	6.13	6.13		6.13
2011 - Collar Contracts with Short Puts [Member]
Volume	200,000	200,000	200,000		200,000
2011 - Collar Contracts with Short Puts [Member] \| Ceiling [Member]
NYMEX price	8.55	8.55	8.55		8.55
2011 - Collar Contracts with Short Puts [Member] \| Floor [Member]
NYMEX price	6.32	6.32	6.32		6.32
2011 - Collar Contracts with Short Puts [Member] \| Short Put [Member]
NYMEX price	4.88	4.88	4.88		4.88
2011 - Basis Swap Contracts [Member]
Volume	143,500	143,500	153,500		146,809
NYMEX price	(0.56)	(0.56)	(0.53)		(0.55)
2012 - Swap Contracts [Member]
Volume	105,000	105,000	105,000	105,000	105,000
NYMEX price	5.82	5.82	5.82	5.82	5.82
2012 - Collar Contracts [Member]
Volume	65,000.00	65,000.00	65,000.00	65,000.00	65,000.00
2012 - Collar Contracts [Member] \| Ceiling [Member]
NYMEX price	6.60	6.60	6.60	6.60	6.60
2012 - Collar Contracts [Member] \| Floor [Member]
NYMEX price	5.00	5.00	5.00	5.00	5.00
2012 - Collar Contracts with Short Puts [Member]
Volume	190,000	190,000	190,000	190,000	190,000
2012 - Collar Contracts with Short Puts [Member] \| Ceiling [Member]
NYMEX price	7.96	7.96	7.96	7.96	7.96
2012 - Collar Contracts with Short Puts [Member] \| Floor [Member]
NYMEX price	6.12	6.12	6.12	6.12	6.12
2012 - Collar Contracts with Short Puts [Member] \| Short Put [Member]
NYMEX price	4.55	4.55	4.55	4.55	4.55
2012 - Basis Swap Contracts [Member]
Volume	116,000	116,000	116,000	116,000	116,000
NYMEX price	(0.37)	(0.37)	(0.37)	(0.37)	(0.37)
2013 - Swap Contracts [Member]
Volume	67,500	67,500	67,500	67,500	67,500
NYMEX price	6.11	6.11	6.11	6.11	6.11
2013 - Collar Contracts [Member]
Volume	150,000	150,000	150,000	150,000	150,000
2013 - Collar Contracts [Member] \| Ceiling [Member]
NYMEX price	6.25	6.25	6.25	6.25	6.25
2013 - Collar Contracts [Member] \| Floor [Member]
NYMEX price	5.00	5.00	5.00	5.00	5.00
2013 - Collar Contracts With Short Puts [Member]
Volume	45,000	45,000	45,000	45,000	45,000
2013 - Collar Contracts With Short Puts [Member] \| Ceiling [Member]
NYMEX price	7.49	7.49	7.49	7.49	7.49
2013 - Collar Contracts With Short Puts [Member] \| Floor [Member]
NYMEX price	6.00	6.00	6.00	6.00	6.00
2013 - Collar Contracts With Short Puts [Member] \| Short Put [Member]
NYMEX price	4.50	4.50	4.50	4.50	4.50
2013 - Basis Swap Contracts [Member]
Volume	32,500	32,500	32,500	32,500	32,500
NYMEX price	(0.34)	(0.34)	(0.34)	(0.34)	(0.34)
2014 - Swap Contracts [Member]
Volume	50,000	50,000	50,000	50,000	50,000
NYMEX price	6.05	6.05	6.05	6.05	6.05
2014 - Collar Contracts [Member]
Volume	140,000	140,000	140,000	140,000	140,000
2014 - Collar Contracts [Member] \| Ceiling [Member]
NYMEX price	6.44	6.44	6.44	6.44	6.44
2014 - Collar Contracts [Member] \| Floor [Member]
NYMEX price	5.00	5.00	5.00	5.00	5.00
2014 - Collar Contracts with Short Puts [Member]
Volume	50,000	50,000	50,000	50,000	50,000
2014 - Collar Contracts with Short Puts [Member] \| Ceiling [Member]
NYMEX price	8.08	8.08	8.08	8.08	8.08
2014 - Collar Contracts with Short Puts [Member] \| Floor [Member]
NYMEX price	6.00	6.00	6.00	6.00	6.00
2014 - Collar Contracts with Short Puts [Member] \| Short Put [Member]
NYMEX price	4.50	4.50	4.50	4.50	4.50
2014 - Basis Swap Contracts [Member]
Volume	10,000	10,000	10,000	10,000	10,000
NYMEX price	(0.16)	(0.16)	(0.16)	(0.16)	(0.16)
2015 - Collar contracts [Member]
Volume	50,000	50,000	50,000	50,000	50,000
2015 - Collar contracts [Member] \| Ceiling [Member]
NYMEX price	7.92	7.92	7.92	7.92	7.92
2015 - Collar contracts [Member] \| Floor [Member]
NYMEX price	5.00	5.00	5.00	5.00	5.00

Derivative Financial Instruments (Fixed-for-Variable Interest Rates) (Details) (Fixed for Variable [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2011
Interest Swap due July 2016 [Member]
Notional Amount	$ 400,000
Weighted Average Fixed Interest Rate	2.87%
Termination Date	July 2016
Interest Swap due March 2017 [Member]
Notional Amount	$ 70,000
Weighted Average Fixed Interest Rate	3.23%
Termination Date	March 2017

Derivative Financial Instruments (Derivative Instruments) (Details) (USD $)
In Thousands, unless otherwise specified

Mar. 31, 2011

Dec. 31, 2010

Total derivatives not designated as hedging instruments, Assets

$ 285,659

^[1]

$ 347,802

^[1]

Total derivatives, Asset

285,659

^[1]

347,802

^[1]

Total derivatives not designated as hedging instruments, Liability

385,348

^[1]

162,683

^[1]

Total derivatives, Liability

385,348

^[1]

162,683

^[1]

Interest Rate Derivatives [Member] | Derivatives Current [Member]

Total derivatives not designated as hedging instruments, Assets

11,810

^[1]

11,903

^[1]

Total derivatives not designated as hedging instruments, Liability

886

^[1]

Interest Rate Derivatives [Member] | Derivatives Noncurrent [Member]

Total derivatives not designated as hedging instruments, Assets

9,306

^[1]

15,762

^[1]

Total derivatives not designated as hedging instruments, Liability

10,745

^[1]

9,227

^[1]

Commodity Price Derivatives [Member] | Derivatives Current [Member]

Total derivatives not designated as hedging instruments, Assets

145,952

^[1]

167,406

^[1]

Total derivatives not designated as hedging instruments, Liability

183,747

^[1]

87,741

^[1]

Commodity Price Derivatives [Member] | Derivatives Noncurrent [Member]

Total derivatives not designated as hedging instruments, Assets

118,591

^[1]

152,731

^[1]

Total derivatives not designated as hedging instruments, Liability

$ 190,856

^[1]

$ 64,829

^[1]

[1]	Derivative assets and liabilities shown in the tables above are presented as gross assets and liabilities, without regard to master netting arrangements which are considered in the presentations of derivative assets and liabilities in the accompanying consolidated balance sheets.

Derivative Financial Instruments (Derivative Obligations Under Terminated Hedge Arrangements) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2011	Mar. 31, 2010
Amount of Gain/(Loss) Reclassified from AOCI into Earnings	$ 8,056	$ 20,926
Amount of Gain (Loss) Recognized in Earnings on Derivatives	(244,432)	266,618
Interest Rate Derivatives [Member] \| Interest Expense [Member]
Amount of Gain/(Loss) Reclassified from AOCI into Earnings	(68)	(1,058)
Interest Rate Derivatives [Member] \| Derivative gains (losses) [Member]
Amount of Gain/(Loss) Reclassified from AOCI into Earnings		(1,142)
Amount of Gain (Loss) Recognized in Earnings on Derivatives	(2,152)	11,399
Commodity Price Derivatives [Member] \| Derivative gains (losses) [Member]
Amount of Gain (Loss) Recognized in Earnings on Derivatives	(242,280)	255,219
Commodity Price Derivatives [Member] \| Oil and gas revenue [Member]
Amount of Gain/(Loss) Reclassified from AOCI into Earnings	$ 8,124	$ 23,126

Asset Retirement Obligations (Asset Retirement Obligations) (Details) (USD $)

3 Months Ended

Mar. 31, 2011

Mar. 31, 2010

Dec. 31, 2010

Asset Retirement Obligations

Beginning asset retirement obligations

$ 152,291,000

$ 166,434,000

Liabilities assumed in acquisitions

6,000

New wells placed on production

671,000

278,000

Changes in estimates

300,000

Disposition of wells

(81,000)

(26,248,000)

Liabilities settled

(1,234,000)

(1,154,000)

Accretion of discount from continuing operations

2,655,000

2,859,000

Accretion of discount from discontinued operations

81,000

^[1]

101,000

^[1]

Ending asset retirement obligations

154,689,000

142,270,000

Asset retirement obligations, current portion

$ 19,400,000

$ 19,900,000

[1]	Represents the significant noncash components of discontinued operations.

Postretirement Benefit Obligations (Accumulated Postretirement Benefit Obligations) (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2011	Mar. 31, 2010	Dec. 31, 2010
Postretirement Benefit Obligations
Beginning accumulated postretirement benefit obligations	$ 7,408,000	$ 9,075,000	$ 9,075,000
Net benefit payments	(316,000)	(312,000)
Service costs	61,000	80,000
Accretion of interest	78,000	108,000
Ending accumulated postretirement benefit obligations	7,231,000	8,951,000	7,408,000
Unfunded accumulated postretirement benefit obligations	$ 7,200,000		$ 7,400,000

- Definition

1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. The projected benefit obligation is measured using assumptions as to future compensation levels if the pension benefit formula is based on those future compensation levels (pay-related, final-pay, final-average-pay, or career-average-pay plans). For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date. Prior to an employee's full eligibility date, the accumulated postretirement benefit obligation as of a particular date for an employee is the portion of the expected postretirement benefit obligation attributed to that employee's service rendered to that date; on and after the full eligibility date, the accumulated and expected postretirement benefit obligations for an employee are the same.

+ References+ Details

Net Income (Loss) Per Share (Reconciliation of Earnings, Basic and Diluted) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2011	Mar. 31, 2010
Income(loss) as reported, Continuing Operations	$ (70,838)	$ 256,795
Income (loss) from discontinued operations, net of tax	414,642	3,811
Net income attributable to common stockholders	348,594	245,254
Net income attributable to the noncontrolling interests	(4,790)	15,352
Participating basic distributed earnings	(6,140)	(5,337)
Basic income (loss) attributable to common stockholders	342,454	239,917
Diluted adjustments earnings		51
Diluted income (loss) attributable to common stockholders	342,454	239,968
Segment, Continuing Operations [Member]
Income(loss) as reported, Continuing Operations	(70,838)	256,795
Net income attributable to the noncontrolling interests	4,790	(15,352)
Participating basic distributed earnings		(5,254)
Basic income (loss) attributable to common stockholders	(66,048)	236,189
Diluted adjustments earnings		50
Diluted income (loss) attributable to common stockholders	(66,048)	236,239
Segment, Discontinued Operations [Member]
Income (loss) from discontinued operations, net of tax	414,642	3,811
Participating basic distributed earnings	(6,140)	(83)
Basic income (loss) attributable to common stockholders	408,502	3,728
Diluted adjustments earnings		1
Diluted income (loss) attributable to common stockholders	$ 408,502	$ 3,729

- Definition

This element represents the overall income (loss) from a disposal group that is classified as a component of the entity, net of income tax, reported as a separate component of income before extraordinary items and the cumulative effect of accounting changes before deduction or consideration of the amount which may be allocable to noncontrolling interests, if any. Includes the following (net of tax): income (loss) from operations during the phase-out period, gain (loss) on disposal, provision (or any reversals of earlier provisions) for loss on disposal, and adjustments of a prior period gain (loss) on disposal.

+ References+ Details

- Definition

The portion of consolidated profit or loss for the period, net of income taxes, which is attributable to the parent. If the entity does not present consolidated financial statements, the amount of profit or loss for the period, net of income taxes.

+ References+ Details

Net Income (Loss) Per Share (Reconciliation of Weighted-Average Common Shares Outstanding, Basic and Diluted) (Details)

3 Months Ended

Mar. 31, 2011

Mar. 31, 2010

Basic

115,869,000

114,655,000

Dilutive common stock options

^[1]

224,000

^[1]

Contingently issuable - performance shares

^[1]

583,000

^[1]

Diluted

115,869,000

115,462,000

Performance Units [Member]

Number of anti-dilutive securities excluded from calculation

416,703

Stock Options [Member]

Number of anti-dilutive securities excluded from calculation

198,463

Stock Issuable [Member]

Number of anti-dilutive securities excluded from calculation

2,898,761

2.875% Convertible Senior Notes [Member]

Senior notes, interest rate

2.875%

[1]

Geographic Operating Segment Information (Schedule of Income Statement by Geographic Operating Segment) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2011	Mar. 31, 2010
Oil and gas	$ 497,130	$ 472,045
Interest and other	32,687	18,008
Gain (loss) on disposition of assets, net	(2,191)	16,943
Revenues and other income	527,626	506,996
Oil and gas production	99,931	86,100
Production and ad valorem taxes	33,296	27,061
Depletion, depreciation and amortization	140,373	144,428
Exploration and abandonments	17,643	16,848
General and administrative	44,106	38,315
Accretion of discount on asset retirement obligations	2,655	2,859
Interest	45,227	47,523
Hurricane activity, net	71	(7,410)
Derivative (gains) losses, net	244,432	(265,476)
Other	17,881	15,946
Costs and expenses, Total	645,615	106,194
Income (loss) from continuing operations before income taxes	(117,989)	400,802
Income tax benefit (provision)	47,151	(144,007)
Income (loss) from continuing operations	(70,838)	256,795
United States [Member]
Oil and gas	475,729	446,664
Interest and other
Gain (loss) on disposition of assets, net		17,419
Revenues and other income	475,729	464,083
Oil and gas production	98,835	85,324
Production and ad valorem taxes	33,296	27,061
Depletion, depreciation and amortization	116,540	115,505
Exploration and abandonments	17,485	16,776
General and administrative
Accretion of discount on asset retirement obligations	2,044	2,237
Interest
Hurricane activity, net	71	(7,410)
Derivative (gains) losses, net
Other	5,159	10,281
Costs and expenses, Total	273,430	249,774
Income (loss) from continuing operations before income taxes	202,299	214,309
Income tax benefit (provision)	(74,851)	(79,294)
Income (loss) from continuing operations	127,448	135,015
South Africa [Member]
Oil and gas	21,401	25,381
Interest and other
Gain (loss) on disposition of assets, net
Revenues and other income	21,401	25,381
Oil and gas production	1,096	776
Production and ad valorem taxes
Depletion, depreciation and amortization	13,685	21,897
Exploration and abandonments	158	72
General and administrative
Accretion of discount on asset retirement obligations	611	622
Interest
Hurricane activity, net
Derivative (gains) losses, net
Other
Costs and expenses, Total	15,550	23,367
Income (loss) from continuing operations before income taxes	5,851	2,014
Income tax benefit (provision)	(1,638)	(564)
Income (loss) from continuing operations	4,213	1,450
Headquarters [Member]
Oil and gas
Interest and other	32,687	18,008
Gain (loss) on disposition of assets, net	(2,191)	(476)
Revenues and other income	30,496	17,532
Oil and gas production
Production and ad valorem taxes
Depletion, depreciation and amortization	10,148	7,026
Exploration and abandonments
General and administrative	44,106	38,315
Accretion of discount on asset retirement obligations
Interest	45,227	47,523
Hurricane activity, net
Derivative (gains) losses, net	244,432	(265,476)
Other	12,722	5,665
Costs and expenses, Total	356,635	(166,947)
Income (loss) from continuing operations before income taxes	(326,139)	184,479
Income tax benefit (provision)	123,640	(64,149)
Income (loss) from continuing operations	$ (202,499)	$ 120,330

Geographic Operating Segment Information (Reconciliation of Assets from Segment to Consolidated) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2011	Dec. 31, 2010
Total consolidated assets	$ 10,025,986	$ 9,679,102
United States [Member]
Segment assets	9,818,634	8,987,141
South Africa [Member]
Segment assets	111,703	134,901
Tunisian [Member]
Segment assets		325,942
Headquarters [Member]
Segment assets	$ 95,649	$ 231,118

Volumetric Production Payments (Deferred Revenue Carrying Values) (Details) (Volumetric Production Payment [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2011
Volumetric Production Payment [Member]
Deferred revenue at December 31, 2010	$ 87,020
Less: 2011 amortization	(11,083)
Deferred revenue at March 31, 2011	$ 75,937

Volumetric Production Payments (Revenue Recognition in Future Periods) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2011	Dec. 31, 2010
Remaining 2011	$ 44,327	$ 44,951
2012	31,610	42,069
Volumetric Production Payment [Member]
Remaining 2011	33,866
2012	42,071
Total deferred revenue recognized in future periods	$ 75,937	$ 87,020

Interest and Other Income (Interest and Other Income) (Details) (USD $)
In Thousands, unless otherwise specified

3 Months Ended

Mar. 31, 2011

Mar. 31, 2010

Interest and Other Income

Alaskan Petroleum Production Tax credits

$ 27,452

^[1]

$ 14,248

^[1]

Drilling and servicing margin

2,878

510

Deferred compensation plan income

867

510

Other income

1,002

691

Equity interest in income of unconsolidated affiliate

298

Interest income

190

384

Insurance claim recovery

1,665

Total interest and other income

$ 32,687

$ 18,008

[1]	The Company earns Alaskan Petroleum Production Tax ("PPT") credits on qualifying capital expenditures. The Company recognizes income from PPT credits when they are realized through cash refunds or sales.

- Definition

This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. Such amount typically reflects adjustments similar to those made in preparing consolidated statements, including adjustments to eliminate intercompany gains and losses, and to amortize, if appropriate, any difference between cost and underlying equity in net assets of the investee at the date of investment.

+ References+ Details

Other Expense (Schedule of Components of Other Expense) (Details) (USD $)
In Thousands, unless otherwise specified

3 Months Ended

Mar. 31, 2011

Mar. 31, 2010

Other Expense

Transportation commitment charge

$ 5,272

^[1]

Excess and terminated rig related costs

5,159

^[2]

10,281

^[2]

Other

2,494

650

Loss on extinguishment of debt

2,367

Contingency and environmental accrual adjustments

1,295

153

Cancelled well costs

991

Inventory impairment

285

^[3]

1,557

^[3]

Bad debt expense

224

Well servicing operations

^[4]

3,081

^[4]

Total other expense

$ 17,881

$ 15,946

[1]	Primarily represents firm transportation contract deficiency payment obligations.
[2]	Represents above market drilling rig costs, idle rig costs and costs incurred to terminate contractual drilling rig commitments prior to their contractual maturities.
[3]	Represents impairment charges on excess materials and supplies inventories.
[4]	Represents idle well servicing costs.

Discontinued Operations (Schedule of Discontinued Operations) (Details) (USD $)

3 Months Ended

1 Months Ended

3 Months Ended

Mar. 31, 2011

Mar. 31, 2010

Feb. 28, 2011

Pioneer Tunisia [Member]

Mar. 31, 2011

Deepwater Leases [Member]

Oil and gas

$ 22,130,000

$ 35,752,000

Interest and other

4,568,000

^[1]

1,795,000

^[1]

2,000,000

Gain on disposition of assets, net

649,872,000

Total revenues and other income from discontinued operations

676,570,000

37,547,000

Oil and gas production

2,126,000

3,616,000

Depletion, depreciation and amortization

^[2]

6,340,000

^[2]

Exploration and abandonments

2,554,000

3,950,000

General and administrative

6,619,000

2,633,000

Accretion of discount on asset retirement obligations

81,000

^[2]

101,000

^[2]

Other

1,182,000

629,000

Total costs and expenses from discontinued operations

12,562,000

17,269,000

Income from discontinued operations before income taxes

664,008,000

20,278,000

Current tax (provision) benefit

(7,574,000)

444,000

Deferred tax provision

(241,792,000)

^[2]

(16,911,000)

^[2]

Income from discontinued operations

414,642,000

3,811,000

Percentage sale of ownership in subsidiary

100.00%

Cash proceeds from sale of subsidiaries, net

845,200,000

Gain on sale of subsidiaries, pretax

$ 649,900,000

[1]	Includes $2.0 million of interest received during the first quarter of 2011 from the Bureau of Ocean Energy Management, Regulation, and Enforcement related to the recovery of excess royalties paid by the Company on qualifying deepwater leases in the Gulf of Mexico.
[2]	Represents the significant noncash components of discontinued operations.

Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2011	Dec. 31, 2010
Valuation allowances	$ 6.6	$ 33.1
Tunisian [Member]
Valuation allowances		$ 26.5

Consolidated Statement of Stockholders' Equity (Parenthetical) (USD $)	3 Months Ended
	Mar. 31, 2011	Mar. 31, 2010
Consolidated Statement of Stockholders' Equity
Dividends declared, per share	$ 0.04	$ 0.04

Volumetric Production Payments (Narrative) (Details) (Volumetric Production Payment [Member])	3 Months Ended
	Mar. 31, 2011
Volumetric Production Payment [Member]
Production/capital costs responsibility, in percentage	100.00%