Asset Retirement Obligations

9 Months Ended

Sep. 30, 2017

Asset Retirement Obligation Disclosure [Abstract]

Asset Retirement Obligations

9. Asset Retirement Obligations

Asset retirement obligations (ARO) consist primarily of estimated costs of dismantlement, removal, site reclamation and similar activities associated with our oil and gas properties. Changes in ARO are as follows:

	Nine Months Ended September 30,
(millions)	2017			2016
Asset Retirement Obligations, Beginning Balance	$	935		$	989
Liabilities Incurred	83			5
Liabilities Settled	(53		)	(87		)
Revision of Estimate	(56		)	4
Accretion Expense (1)	35			37
Asset Retirement Obligations, Ending Balance	$	944		$	948

⁽¹⁾  Accretion expense is included in depreciation, depletion and amortization (DD&A)expense in the consolidated statements ofoperations.

For the Nine Months Ended September 30, 2017Liabilities incurred include $58 million related to the Clayton Williams Energy Acquisition and $25 million primarily for other US onshore wells and facilities placed into service. Liabilities settled include $37 million related to abandonment of onshore US properties, $12 million related to properties sold in the Marcellus Shale upstream divestiture and $4 million related to other offshore international and US properties. Revisions of estimates relate to decreases in cost and timing estimates of $42 million associated with the North Sea abandonment project and $29 million for US onshore and Gulf of Mexico, partially offset by an increase of $15 million for West Africa.

For theNine Months Ended September 30, 2016Liabilities incurred were due to new wells and facilities for onshore US. Liabilities settled primarily related to Gulf of Mexico and onshore US property abandonments.