Asset Retirement Obligations

12 Months Ended

Dec. 31, 2011

Asset Retirement Obligations [Abstract]

Asset Retirement Obligations

Note 11.  Asset Retirement Obligations

Changes in asset retirement obligations were as follows:

	Year Ended December 31,
	2011			2010
(millions)
Asset Retirement Obligations, Beginning Balance	$	253		$	232
Liabilities Incurred		23			17
Liabilities Settled		(24	)		(56	)
Revision of Estimate		105			43
Accretion Expense		20			17
Asset Retirement Obligations, Ending Balance	$	377		$	253

For the year ended December 31, 2011, liabilities incurred were primarily due to the Marcellus Shale asset acquisition as well as additions for the Alen project in Equatorial Guinea and Lochranza project in the North Sea. Liabilities settled related to deepwater and shelf properties in the Gulf of Mexico. Revisions resulted from changes in estimated abandonment costs mainly in the DJ Basin and deepwater Gulf of Mexico.

For the year ended December 31, 2010, liabilities incurred were primarily due to the DJ Basin asset acquisition.   Liabilities settled related to non-core onshore US properties sold, abandoned Gulf of Mexico shelf assets, and Block 3 offshore Ecuador. Revisions resulted from changes in estimated timing of actual abandonment due to shortened field lives for certain UK assets and overall cost increases for assets located primarily in the deepwater Gulf of Mexico.

Accretion expense is included in DD&Aexpense in the consolidated statements ofoperations.