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ASSET RETIREMENT OBLIGATIONS (Tables)
 12 Months Ended
Dec. 31, 2012
Asset Retirement Obligations

The change in our asset retirement obligations during 2012, 2011 and 2010 is set forth below:

 

     Year Ended December 31,  
     2012     2011     2010  

Asset retirement obligations as of the beginning of the year, including current portion

    $ 425,779      $ 373,920      $ 320,599   

Liabilities incurred

      3,869        7,993        1,528   

Liabilities settled

      (67,641 )      (63,226 )      (36,392 ) 

Liabilities assumed

      15,263        59,441        —     

Divestment of properties

      (7,563 )      (10,900 )      (692 ) 

Accretion expense

      33,331        30,764        34,469   

Revision of estimates

      85,264        27,787        54,408   
  

 

 

    

 

 

    

 

 

  

Asset retirement obligations as of the end of the year, including current portion

    $ 488,302      $ 425,779      $ 373,920