Asset Retirement Obligations

6 Months Ended

Jun. 30, 2019

Asset Retirement Obligation Disclosure [Abstract]

Asset Retirement Obligations

Note 6. 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)	2019			2018
Asset Retirement Obligations, Beginning Balance	$	880		$	875
Liabilities Incurred	15			14
Liabilities Settled	(56		)	(261		)
Revisions of Estimates	(70		)	(10		)
Accretion Expense	23			17
Asset Retirement Obligations, Ending Balance	$	792		$	635

Six Months Ended June 30, 2019 Liabilities settled relate to abandonment of US onshore properties, primarily in the DJ Basin where we have engaged in a program to plug and abandon older vertical wells. Costs associated with these abandonment activities will be incurred over several years. Revisions of estimates relate primarily to a decrease of $73 million in the DJ Basin as a result of improved cycle times and cost reductions for vertical wells.

Six Months Ended June 30, 2018 Liabilities settled include $216 million of liabilities assumed by the purchaser of the Gulf of Mexico assets and $44 million related to abandonment of US onshore properties, primarily in the DJ Basin. Revisions of estimates relate primarily 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 in cost and timing estimates of $7 million for US onshore.