Supplementary information (Tables)

3 Months Ended

Mar. 31, 2013

Supplemental Information Disclosure Abstract

Schedule of costs incurred in the acquisition and development of oil and natural gas assets

Costs incurred in the acquisition and development of oil and natural gas assets are presented below for the periods presented:



	Three months ended March 31,
(in thousands)	2013		2012
Property acquisition costs:
Proved	$	—	$	—
Unproved	—		—
Exploration	8,761		29,467
Development costs⁽¹⁾	157,316		195,091
Total costs incurred	$	166,077	$	224,558

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(1)	The costs incurred for oil and natural gas development activities include $0.6 million and $0.9 million in asset retirement obligations for the three months ended March 31, 2013 and 2012, respectively.

- Definition

Tabular disclosure of the aggregate of costs (whether the costs are capitalized or charged to expense at the time they are incurred ) incurred for the year in oil and gas property acquisition, exploration and development activities.

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