Asset Retirement Obligations

6 Months Ended

Jun. 30, 2018

Asset Retirement Obligation Disclosure [Abstract]

Asset Retirement Obligations

Note 8. 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:

	Six Months Ended June 30,
(millions)	2018			2017
Asset Retirement Obligations, Beginning Balance	$	875		$	935
Liabilities Incurred	14			82
Liabilities Settled	(261		)	(32		)
Revisions of Estimates	(10		)	(15		)
Accretion Expense (1)	17			23
Asset Retirement Obligations, Ending Balance	$	635		$	993

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

For the Six Months Ended June 30, 2018 Liabilities settled include $216 million of liabilities assumed by the purchaser of the Gulf of Mexico properties and $44 million related to abandonment of US onshore properties, primarily in the DJ Basin. Revisions of estimates primarily relate to decreases in cost and timing estimates of $11 million associated with the North Sea abandonment project and $6 million for Eastern Mediterranean, partially offset by an increase of $7 million for US onshore.

For the Six Months Ended June 30, 2017 Liabilities incurred include $59 million related to the Clayton Williams Energy Acquisition and $23 million primarily for other US onshore wells and facilities placed into service. Liabilities settled primarily related to US onshore property abandonments, as well as $12 million related to properties sold in the Marcellus Shale upstream divestiture. Revisions of estimates related to decreases in cost and timing estimates of $30 million for US onshore and Gulf of Mexico, partially offset by an increase of $15 million for West Africa.