The Marcellus shale in West Virginia, Pennsylvania, and New York, once thought to be played out, is now estimated to hold 168-516 TCF still available with horizontal drilling.

It has been suggested that the Marcellus shale and other Devonian shales of the Appalachian Basin, could supply the northeast U.S. with natural gas. The shale contains largely untapped natural gas reserves, and its proximity to the high-demand markets along the U.S. east coast makes it an attractive target for energy development.

To extract the shale gas at more commercially viable rates, directional drilling is done to depths of 7,000 to 10,000 ft (2,100 to 3,000 m) underground to reach the formation, and then water and chemicals are pumped into the rock under high pressure in a process known as hydraulic fracturing to release the gas from the low permeability shale.