Quarterly report pursuant to Section 13 or 15(d)

Asset Retirement Obligations

Asset Retirement Obligations
9 Months Ended
Sep. 30, 2018
Asset Retirement Obligation [Abstract]  
Asset Retirement Obligations
Asset Retirement Obligations

The table below summarizes the activity for the Company’s ARO:
Nine Months Ended
September 30, 2018
Asset retirement obligations at January 1, 2018

Accretion expense

Liabilities incurred

Liabilities settled
Revisions to estimate (a)

Asset retirement obligations at end of period

Less: Current asset retirement obligations
Long-term asset retirement obligations at September 30, 2018

Revisions to estimated ARO obligations can result from changes in retirement cost estimates, revisions to estimated inflation rates and changes in the estimated timing of abandonment.

Certain of the Company’s operating agreements require that assets be restricted for abandonment obligations. Amounts recorded in the consolidated balance sheet at September 30, 2018 as long-term restricted investments were $3,413. These assets, which primarily include short-term U.S. Government securities, are held in abandonment trusts dedicated to pay future abandonment costs for several of the Company’s oil and natural gas properties.