The following table provides a summary of changes in asset retirement obligations:


	Year Ended December 31,
thousands	2024		2023
Carrying amount of asset retirement obligations at beginning of year	$	366,791	$	300,514
Liabilities incurred	10,060		34,929
Liabilities settled	(5,970)		(11,273)
Accretion expense	19,432		15,040
Revisions in estimated liabilities	(7,288)		27,581
Carrying amount of asset retirement obligations at end of year	$	383,025	$	366,791

Liabilities incurred for the year ended December 31, 2024, primarily related to expansion activity in West Texas. Revisions in estimated liabilities for the year ended December 31, 2024, primarily related to a decrease in expected settlement costs for certain assets in the Rocky Mountains.

Liabilities incurred for the year ended December 31, 2023, primarily related to the acquisition of Meritage and expansion activity in West Texas. Revisions in estimated liabilities for the year ended December 31, 2023, primarily related to an increase in expected settlement costs across all areas of operations.