We are the third-largest producer of natural gas in the United States (second among independents). We own interests in approximately 39,200 producing natural gas and oil wells that are currently producing approximately 2.3 billion cubic feet equivalent, or bcfe, per day, of which 92% is natural gas. Our strategy is focused on discovering, acquiring, and developing conventional and unconventional natural gas reserves onshore in the U.S., east of the Rocky Mountains.
Our most important operating area has historically been in the Mid-Continent region of Oklahoma, Arkansas, southwestern Kansas and the Texas Panhandle. At March 31, 2008, 47% of our estimated proved natural gas and oil reserves were located in the Mid Continent Region. During the past five years, we have also built significant positions in various conventional and unconventional plays in the Fort Worth Basin in north-central Texas; the Appalachian Basin, principally in West Virgina, eastern Kentucky, eastern Ohio, Pennsylvania and southern New York; the Permian and Delaware Basins of West Texas and eastern New Mexico; the Ark-La-Tex area of East Texas and northern Louisiana; and the South Texas and Texas Gulf Coast regions. We have established a top-three position in nearly every major unconventional play onshore in the U.S. east of the Rockies, including the Barnett Shale, the Arkansas Fayetteville Shale, the Louisiana Haynesville Shale, the Appalachian Basin Devonian and Marcellus Shales, the Delaware Basin Barnett and Woodford Shales in West Texas, and the Alabama Conasauga and Chattanooga Shales.
Our proved natural gas and oil reserves have increased over nine-fold from 1.2 tcfe in 1999 to 11.5 tcfe as of March 31, 2008. Similarly, since 1999 our average daily production has grown at an annualized rate of 25% to approximately 2.3 bcfe per day, of which 92% is natural gas. We own interests in approximately 39,200 producing natural gas and oil wells and have built what we believe is the largest combined inventories of onshore leasehold (13.9 million net acres) and 3-D seismic data (20.0 million acres) in the U.S. On this leasehold, the company has approximately 33,700 net drillsites, representing more than a 10-year inventory of drilling projects, on which we believe we can develop approximately 4.0 tcfe of proved undeveloped reserves and approximately 37.2 tcfe of risked unproved reserves. Chesapeake's 11.5 tcfe of estimated proved reserves and it's 37.2 tcfe of estimated risked unproved reserves together total approximately 49 tcfe.