hale rock formations can be found scattered coast to coast. The map at right shows where basins within these formations have been determined to contain oil and gas.
The geology of many basins makes extraction of natural gas too expensive or complicated to tap, however. Areas where large amounts of gas has accumulated, where extraction is considered both technically possible and profitable, are called "plays." Two of the most prolific plays to date include the Barnett Shale in Texas and the Marcellus Shale, which runs from southern New York, across much of Pennsylvania, and as far south as Virginia. Only a handful of plays are producing the majority of shale gas in the U.S.