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Asset Retirement Obligation
12 Months Ended
Dec. 31, 2012
Assets Retirement Obligation [Abstract]  
Asset Retirement Obligation
NOTE 6—Asset Retirement Obligation
 
The following table describes changes in our asset retirement liability during each of the years ended December 31, 2012 and 2011. The ARO liability in the table below includes amounts classified as both current and long-term at December 31, 2012 and 2011.
 
   
North America
Years Ended
December 31
  
South America
Years Ended
December 31
 
   
2012
  
2011
  
2012
  
2011
 
ARO liability at January 1
 $7,320  $5,481  $34,099  $9,960 
Accretion expense
  552   1,839   372   14,607 
Liabilities incurred from drilling
           9,532 
Liabilities settled—assets sold
        (34,471)   
Changes in estimates
            
                  
ARO liability at December 31,
 $7,872  $7,320  $  $34,099