A roll-forward of our asset retirement obligation is as follows (in thousands):


	Year Ended December 31,
	2024		2023
Balance, beginning of year	$	336,832	$	291,026
Additional liabilities incurred with development activities and other	8,556		7,516
Additional liabilities incurred with acquisitions	37,251		40,373
Liabilities settled	(46,526)		(19,136)
Accretion expense	23,327		17,053
Revisions to estimate(1)	126,174		—
Obligations discharged with divestitures	(27,976)		—
Balance, end of year	$	457,638	$	336,832
Current portion(2)	58,636		31,116
Long-term portion	399,002		$	305,716

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(1)Revisions to estimates for the year ended December 31, 2024 were primarily a result of (a) increases in our estimated plugging and abandonment cost driven by increased regulatory burden, service costs, complexity of plugging activities, and reclamation and environmental obligations that arose from normal operation of the assets, as evidenced through our plugging program activities during 2024, particularly in the DJ Basin, and (b) the acceleration of the estimated settlement date for certain wells.