The Marcellus Shale encompasses about 95,000 square miles and extends in the subsurface from New York State in the north to northeastern Kentucky and Tennessee in the south. It is the most prolific natural gas-producing formation in the Appalachian Basin.

EIA estimates proven reserves in the Marcellus Play of 77.2 trillion cubic feet (Tcf) at year end 2015 which makes it one of the largest natural gas plays in the U.S. The Marcellus has oil reserves of 143 million barrels (MMbbls).