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Subsequent events
3 Months Ended
Mar. 31, 2012
Subsequent events [Abstract]  
Subsequent events
10. Subsequent events

On April 13, 2012, NYMEX crude oil futures prices exceeded $100 for the 61 st consecutive day. Accordingly, the Company incurred a payable for additional acquisition costs under the third quarter 2011 acquisition agreement described in Note 3. This payable has a payment due date of April 13, 2013.