For many years, natural gas companies have been producing the fuel from "conventional" gas reservoirs, relatively close to the surface and easily accessible. New shale gas production techniques have opened much wider areas for exploration, including the Marcellus area in Pennsylvania and the Barnett and Haynesville areas in Texas.
Conventional natural gas drilling areas are sized by 2008 natural gas production. The Marcellus shale drilling area overlaps with the Devorian and Utica formations. Shale plays and shale basin locations updated as of 2011. Conventional drilling locations as of 2009.