The following table presents the balance and activity of the asset retirement obligations for the years ended December 31, 2013, 2012 and 2011 (in thousands).



	2013			2012			2011
Asset retirement obligations at January 1	$	498,410		$	128,116		$	119,877
Liability incurred upon acquiring and drilling wells	5,078			7,479			5,716
Liability assumed in acquisition(1)	—			371,365			—
Revisions in estimated cash flows	(3,077		)	34,654			7,574
Liability settled or disposed in current period(2)	(113,071		)	(72,200		)	(14,419		)
Accretion(3)	36,777			28,996			9,368
Asset retirement obligations at December 31	424,117			498,410			128,116
Less: current portion	87,063			118,504			32,906
Asset retirement obligations, net of current	$	337,054		$	379,906		$	95,210

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(1)	Represents asset retirement obligations assumed in the acquisitions of oil and natural gas properties in the Gulf of Mexico during the second quarter of 2012.

(2)

Year ended December 31, 2013 includes $45.3 million for the decommissioning of various platforms, pipeline and associated wells in the Gulf of Mexico and $15.2 million of asset retirement obligations disposed in conjunction with the sale of the Permian Properties. Years ended December 31, 2013 and 2012 include the settlement of plugging and abandonment obligations associated with properties in the Gulf of Mexico. Year ended December 31, 2011 includes amounts related to the Permian Basin and east Texas properties sold during 2011.


(3)	Years ended December 31, 2013 and 2012 include accretion attributable to asset retirement obligations assumed in the acquisitions of oil and natural gas properties in the Gulf of Mexico during the second quarter of 2012.