Annual report pursuant to Section 13 and 15(d)

Estimated Quantities of Net Proved, Proved Developed and Proved Undeveloped Oil, Ngls and Natural Gas Reserves (Detail)

v2.4.0.6
Estimated Quantities of Net Proved, Proved Developed and Proved Undeveloped Oil, Ngls and Natural Gas Reserves (Detail)
 12 Months Ended
Dec. 31, 2012
MMBbls
Dec. 31, 2011
MMBbls
Dec. 31, 2010
MMBbls
Oil | Mmbbls
      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 51.4 [1] 34.0 [1] 31.2 [1]
Revisions of previous estimates (1.1) [1],[2] 0.8 [1],[3] (0.2) [1],[4]
Extensions and discoveries 8.2 [1],[5] 2.0 [1],[6] 1.2 [1],[7]
Purchase of minerals in place 2.5 [1],[8] 20.7 [1],[9] 7.7 [1],[10]
Production (6.0) [1] (6.1) [1] (5.9) [1]
Proved reserves, ending balance 54.8 [1] 51.4 [1] 34.0 [1]
Sales of reserves (0.2) [1],[11]    
Oil | Proved Developed Reserves | Mmbbls
      
Reserve Quantities [Line Items]      
Proved reserves, ending balance 35.3 [1] 23.4 [1] 23.6 [1]
Oil | Proved Undeveloped Reserves | Mmbbls
      
Reserve Quantities [Line Items]      
Proved reserves, ending balance 19.5 [1] 28.0 [1] 10.4 [1]
NGLs | Mmbbls
      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 17.1 [1] 4.2 [1] 3.0 [1]
Revisions of previous estimates (2.6) [1],[2] 5.5 [1],[3] 1.2 [1],[4]
Extensions and discoveries 2.6 [1],[5] 0.4 [1],[6] 0.5 [1],[7]
Purchase of minerals in place 0.2 [1],[8] 8.9 [1],[9] 0.7 [1],[10]
Production (2.1) [1] (1.9) [1] (1.2) [1]
Proved reserves, ending balance 15.2 [1] 17.1 [1] 4.2 [1]
Sales of reserves    [1],[11]    
NGLs | Proved Developed Reserves | Mmbbls
      
Reserve Quantities [Line Items]      
Proved reserves, ending balance 11.0 [1] 11.0 [1] 3.4 [1]
NGLs | Proved Undeveloped Reserves | Mmbbls
      
Reserve Quantities [Line Items]      
Proved reserves, ending balance 4.2 [1] 6.1 [1] 0.8 [1]
Natural Gas | MMcf
      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 289,700 [1] 256,300 [1] 165,800 [1]
Revisions of previous estimates (4,800) [1],[2] 13,500 [1],[3] 14,600 [1],[4]
Extensions and discoveries 29,600 [1],[5] 17,700 [1],[6] 19,100 [1],[7]
Purchase of minerals in place 25,500 [1],[8] 55,900 [1],[9] 101,500 [1],[10]
Production (53,800) [1] (53,700) [1] (44,700) [1]
Proved reserves, ending balance 285,100 [1] 289,700 [1] 256,300 [1]
Sales of reserves (1,100) [1],[11]    
Natural Gas | Proved Developed Reserves | MMcf
      
Reserve Quantities [Line Items]      
Proved reserves, ending balance 243,500 [1] 251,400 [1] 229,100 [1]
Natural Gas | Proved Undeveloped Reserves | MMcf
      
Reserve Quantities [Line Items]      
Proved reserves, ending balance 41,600 [1] 38,300 [1] 27,200 [1]
Barrel Equivalent | Mmboe
      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 116.9 [12] 80.9 [12] 61.8 [12]
Revisions of previous estimates (4.6) [12],[2] 8.6 [12],[3] 3.4 [12],[4]
Extensions and discoveries 15.7 [12],[5] 5.3 [12],[6] 4.9 [12],[7]
Purchase of minerals in place 7.0 [12],[8] 39.0 [12],[9] 25.3 [10],[12]
Production (17.1) [12] (16.9) [12] (14.5) [12]
Proved reserves, ending balance 117.5 [12] 116.9 [12] 80.9 [12]
Sales of reserves (0.4) [11],[12]    
Barrel Equivalent | Proved Developed Reserves | Mmboe
      
Reserve Quantities [Line Items]      
Proved reserves, ending balance 86.9 [12] 76.4 [12] 65.2 [12]
Barrel Equivalent | Proved Undeveloped Reserves | Mmboe
      
Reserve Quantities [Line Items]      
Proved reserves, ending balance 30.6 [12] 40.5 [12] 15.7 [12]
Natural Gas Equivalent | MMcfe
      
Reserve Quantities [Line Items]      
Proved reserves, beginning balance 701,100 [12] 485,400 [12] 371,000 [12]
Revisions of previous estimates (27,500) [12],[2] 51,100 [12],[3] 20,200 [12],[4]
Extensions and discoveries 94,500 [12],[5] 32,000 [12],[6] 29,200 [12],[7]
Purchase of minerals in place 42,000 [12],[8] 234,100 [12],[9] 152,000 [10],[12]
Production (102,800) [12] (101,500) [12] (87,000) [12]
Proved reserves, ending balance 705,100 [12] 701,100 [12] 485,400 [12]
Sales of reserves (2,200) [11],[12]    
Natural Gas Equivalent | Proved Developed Reserves | MMcfe
      
Reserve Quantities [Line Items]      
Proved reserves, ending balance 521,200 [12] 458,200 [12] 391,300 [12]
Natural Gas Equivalent | Proved Undeveloped Reserves | MMcfe
      
Reserve Quantities [Line Items]      
Proved reserves, ending balance 183,900 [12] 242,900 [12] 94,100 [12]
[1] Estimated reserves as of December 31, 2012, 2011, 2010 and 2009 are based on the unweighted average of first-day-of-the-month commodity prices over the period January through December for those years in accordance with current definitions and guidelines set forth by the SEC and the FASB.
[2] Includes downward revisions due to price of 8.0 Bcfe and negative performance revisions of 17.9 Bcfe at our Yellow Rose Properties.
[3] Includes revision of 6.3 Bcfe due to an increase in average prices; 16.5 Bcfe for a change in NGLs marketing arrangements; 11.3 Bcfe increase due to additional compression at our Tahoe field that increases production and ultimate recoveries; and 10.6 Bcfe at our Fairway field for revisions to reserve estimates from the acquisition date to year end.
[4] Includes revisions due to price of 17.5 Bcfe.
[5] Includes extensions and discoveries of 69.5 Bcfe at our Yellow Rose Properties and extensions and discoveries of 16.2 Bcfe at our High Island 22 field
[6] Includes discoveries of 13.9 Bcfe at our Main Pass 98 field and 8.0 Bcfe at our Ship Shoal 349/359 field and extensions of 3.7 Bcfe at our Main Pass 108 field.
[7] Includes discoveries of 21.9 Bcfe primarily in the Main Pass 108, Main Pass 98 and Main Pass 283 fields and extensions of 7.2 Bcfe primarily in the Main Pass 283 field.
[8] Due to the acquisition of the Newfield Properties.
[9] Primarily due to the acquisition of the Yellow Rose Properties and the Fairway Properties.
[10] Primarily due to the acquisition of the Total Properties and the Tahoe Properties.
[11] Due to the sale of our interest in the South Timbalier 41 field.
[12] The conversion to barrels of oil equivalent and cubic feet equivalent were determined using the energy-equivalent ratio of six Mcf of natural gas to one Bbl of crude oil, condensate or NGLs (totals may not compute due to rounding). The energy-equivalent ratio does not assume price equivalency, and the energy-equivalent prices for oil, NGLs and natural gas may differ significantly