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Commitments (Tables)
12 Months Ended
Dec. 31, 2012
Commitments [Abstract]  
Future minimum lease payments for non-cancelable operating leases
         

(Thousands of dollars)

  Operating
Leases
 

2013

  $ 662  

2014

    261  

2015

    122  
   

 

 

 

Total minimum payments

  $ 1,045  
   

 

 

 
Reconciliation of the liability for plugging and abandonment costs
                 
    Year Ended December 31,  

(Thousands of dollars)

      2012             2011      

Asset retirement obligation at beginning of period

  $ 19,013     $ 17,147  

Liabilities incurred

    733       398  

Liabilities settled

    (15,361     (421

Accretion expense

    1,053       1,015  

Revisions in estimated liabilities

    3,574       874  
   

 

 

   

 

 

 

Asset retirement obligation at end of period

  $ 9,012     $ 19,013