The following table presents the changes in our estimated future development costs for the years ended December 31, 2012 and 2013: Our estimated future capital costs to develop proved undeveloped reserves as of December 31, 2013 of $543.2 million increased by $89.8 million from our estimated future capital costs of $453.4 million as of December 31, 2012. We incurred approximately $105.7 million during 2013 to develop proved undeveloped reserves, primarily in our Eagle Ford shale properties. Our oil focused future capital expenditures increased by $114.5 million and our natural gas focused capital expenditures increased by $68.2 million. Our estimated future capital costs to develop proved undeveloped reserves as of December 31, 2012 of $453.4 million decreased by $896.8 million from our estimated future capital costs of $1.4 billion as of December 31, 2011. During 2012, we incurred approximately $43.4 million to develop proved undeveloped reserves in our Eagle Ford shale properties. Our oil focused future capital expenditures increased by $174.2 million and our natural gas focused capital expenditures decreased by $954.8 million. Approximately $749.0 million of the reduction in our estimated future development costs in 2012 was associated with wells that, as of December 31, 2011, had positive undiscounted cash flows but had a rate of return of less than 10%. The estimates of our oil and natural gas reserves were determined by Lee Keeling and Associates, Inc. (“Lee Keeling”), an independent petroleum engineering firm. Lee Keeling has been providing consulting engineering and geological services for over fifty years. Lee Keeling’s professional staff is comprised of qualified petroleum engineers who are experienced in all productive areas of the United States. The technical person responsible for review of our reserve estimates at Lee Keeling meets the requirements regarding qualifications, independence, objectivity and confidentiality set forth in the Standards Pertaining to Estimating and Auditing of Oil and Gas Reserves Information promulgated by the Society of Petroleum Engineers. Lee Keeling does not own any interests in our properties and is not employed on a contingent fee basis. We have established, and maintain, internal controls designed to provide reasonable assurance that the estimates of proved reserves are computed and reported in accordance with rules and regulations promulgated by the SEC. These internal controls include documented process workflows, employing qualified professional engineering and geological personnel, and on-going education for personnel involved in our reserves estimation process. Our internal audit function routinely tests our processes and 17 Haynesville/ Bossier Shale Eagle Ford Shale All Other Properties Total (in millions) Total as of December 31, 2011 ................... $886.1 $ 218.0 $ 246.1 $1,350.2 Development Costs Incurred .................... (24.7) (43.4) — (68.1) Sales and Disposals ............................ — — (48.1) (48.1) Additions and Revisions ........................ (777.5) 174.2 (177.3) (780.6) Total Changes ............................ (802.2) 130.8 (225.4) (896.8) Total as of December 31, 2012 ................... 83.9 348.8 20.7 453.4 Development Costs Incurred .................... — (105.7) — (105.7) Additions and Revisions ........................ 68.2 114.5 12.8 195.5 Total Changes ............................ 68.2 8.8 12.8 89.8 Total as of December 31, 2013 ................... $152.1 $ 357.6 $ 33.5 $ 543.2