properties in South Texas. The proved undeveloped reserves associated with our Haynesville and Bossier shale properties represented approximately 87 Bcf of our proved undeveloped natural gas reserves at December 31, 2013. The remaining proved undeveloped natural gas reserves are primarily associated with developing reserves in our Wilcox and Vicksburg reservoirs in South Texas. In 2013, we focused on drilling oil properties due to the weak natural gas prices. 28 of the Eagle Ford shale wells we drilled in 2013 resulted in conversions of proved undeveloped reserves to proved developed producing reserves at December 31, 2013. Our proved undeveloped oil reserves decreased by 2.4 MMBbls during 2013. This decrease was primarily due to converting 3.0 MMBbls of our proved undeveloped oil reserves to developed in 2013 and new reserves additions of 0.6 MMBbls. Our proved undeveloped natural gas reserves increased by 33 Bcf at December 31, 2013 as compared with December 31, 2012. This increase was primarily related to reserve additions of 36 Bcf of natural gas which were partially offset by undeveloped reserves converted to developed reserves of 3 Bcf. As of December 31, 2012, our proved undeveloped reserves included 10.5 MMBbls of oil and 75 Bcf of natural gas, for a total of 138 Bcfe of undeveloped reserves. All of our undeveloped oil reserves and 7 Bcf of natural gas were associated with our Eagleville shale properties in South Texas. The proved undeveloped natural gas reserves associated with our Haynesville and Bossier shale properties represented approximately 55 Bcf of our total natural gas proved undeveloped reserves at December 31, 2012. The remaining proved undeveloped reserves are primarily associated with developing reserves in our Cotton Valley and Hosston sand reservoirs in East Texas/North Louisiana and our Wilcox and Vicksburg reservoirs in South Texas. In 2012, we focused on drilling oil wells due to the weak natural gas prices. Seven of the Eagleville wells we drilled in 2012 resulted in conversions of proved undeveloped reserves to proved developed producing reserves at December 31, 2012. Our oil proved undeveloped reserves increased by 3.8 MMBbls during 2012. This increase was primarily due to our drilling program which added 8.1 MMBbls in the Eagle Ford shale. Sales of oil reserves in 2012 of 3.1 MMbls and conversions of proved developed oil reserves of 1.3 MMBbls partially offset the increase from reserve adds. Our natural gas proved undeveloped reserves decreased by 459 Bcf during 2012. This decrease was primarily related to the decline of natural gas prices which caused 465 Bcf of our natural gas proved undeveloped reserves to become uneconomical under the natural gas prices used to determine proved reserves in 2012. The following table presents the changes in our estimated proved undeveloped oil and natural gas reserves for the years ended December 31, 2011, 2012 and 2013: 15 Proved Undeveloped Reserves 2011 2012 2013 Oil (MBbls) Natural Gas (MMcf) Oil (MBbls) Natural Gas (MMcf) Oil (MBbls) Natural Gas (MMcf) 1,258 518,824 6,735 534,017 10,510 75,019 — — (3,143) (16,125) — — — 11,651 — — — — 5,151 66,978 8,142 7,007 583 36,578 — (39,761) (1,341) (1,095) (3,060) (2,930) 326 (23,675) 117 (448,785) 29 (292) 5,477 15,193 3,775 (458,998) (2,448) 33,356 6,735 534,017 10,510 75,019 8,062 108,375 Beginning Balance ......... Sales and Disposals ........ Acquisitions .............. Extension & Discoveries .... Conversions from undeveloped to developed .............. Price, Performance and Other Revisions .............. Total Change ............. Ending Balance ...........