Investment in Oil and Gas Properties (Tables)

12 Months Ended

Dec. 31, 2011

Investment in Oil and Gas Properties [Abstract]

Financial data relative to oil and gas producing activities

		$000,000,00			$000,000,00			$000,000,00
	Year Ended December 31,
	2011			2010			2009
Oil and gas properties, proved and unevaluated:
Balance, beginning of year	$	6,202,758		$	5,741,081		$	5,409,770
Costs incurred during the year (capitalized):
Acquisition costs, net of sales of unevaluated properties		270,354			127,069			9,072
Exploratory costs		84,199			42,205			78,582
Development costs (1)		426,355			241,387			199,375
Salaries, general and administrative costs		24,430			20,521			19,107
Interest		42,033			30,783			25,573
Less: overhead reimbursements		(352	)		(288	)		(398	)
Total costs incurred during the year, net of divestitures		847,019			461,677			331,311
Balance, end of year	$	7,049,777		$	6,202,758		$	5,741,081
Accumulated depreciation, depletion and amortization (DD&A):
Balance, beginning of year	($	4,804,949	)	($	4,555,372	)	($	3,781,600	)
Provision for DD&A		(276,480	)		(242,745	)		(253,790	)
Write-down of oil and gas properties		—			—			(508,989	)
Sale of proved properties		(93,300	)		(6,832	)		(10,993	)
Balance, end of year	($	5,174,729	)	($	4,804,949	)	($	4,555,372	)
Net capitalized costs, proved and unevaluated	$	1,875,048		$	1,397,809		$	1,185,709
DD&A per Mcfe	$	3.54		$	3.18		$	3.23

(1) Includes asset retirement costs of $96,386, $56,444 and $78,387, respectively.

Oil and gas related operating costs incurred during the year, expensed

		$000,000,000,		$000,000,000,		$000,000,000,
Costs incurred during the year (expensed):
Lease operating expenses	$	179,475	$	152,326	$	156,786
Production taxes		9,380		5,808		7,920
Accretion expense		30,764		34,469		39,306
Expensed costs	$	219,619	$	192,603	$	204,012

Net costs incurred in unevaluated properties located

		$000,000,000			$000,000,000		$000,000,000
	Year Ended December 31,
	2011			2010		2009
Unevaluated oil and gas properties:
Net costs incurred (evaluated) during year:
Acquisition costs	($	2,397	)	$	42,664	($	203,776	)
Exploration costs		(51,207	)		10,491		15,337
Capitalized interest		42,033			30,783		23,943
	($	11,571	)	$	83,938	($	164,496	)

Financial data associated with unevaluated costs

	Balance as of December 31, 2011		Net Costs Incurred During the Year Ended December 31,
			2011		2010		2009		2008 and prior
Acquisition costs	$	245,771	$	61,496	$	108,344	$	9,603	$	66,328
Exploration costs		99,542		55,931		9,658		33,953		—
Capitalized interest		56,296		19,232		28,226		5,002		3,836
Total unevaluated costs	$	401,609	$	136,659	$	146,228	$	48,558	$	70,164