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Asset Retirement Obligation
 12 Months Ended
Dec. 31, 2013
Asset Retirement Obligation  
Asset Retirement Obligation

8. Asset Retirement Obligation

        Activity related to the Company's asset retirement obligation is as follows:

(In thousands)
  Year Ended
December 31, 2013		  

Balance at beginning of period

   $ 67,016  

Liabilities incurred

     5,295  

Liabilities settled

     (762 )

Liabilities divested

     (6,400 )

Accretion expense

     3,691  

Change in estimate

     7,013  
       
​ ​ ​ ​ ​

Balance at end of period

   $ 75,853  
       
​ ​ ​ ​ ​
​ ​ ​ ​ ​
       

        The change in estimate during 2013 is attributable to increased costs for services and related materials to plug and abandon wells in certain areas of our operations. As of December 31, 2013, approximately $2.0 million, which represents the current portion of the Company's asset retirement obligation, is included in accrued liabilities in the Consolidated Balance Sheet.