The United States Geological Survey (USGS) recently estimated that the Marcellus shale has 84 trillion cubic feet of undiscovered natural gas. In addition, the USGS estimates that there are 3.4 billion barrels of untapped natural gas liquids in Marceullus.

The new estimates differ from the figures released in the last USGS assessment performed in 2002, another estimate published in 2009 by a professor of geosciences and predictions made by a 2009 Department of Energy – National Energy Technology Laboratory (NTEL) report.

The 2002 assessment predicted the Marcellus shale contained 2 trillion cubic feet of natural gas along with 0.01 billion barrels of natural gas liquids.

A NTEL report released in April 2009 estimated that the formation contains 262 trillion cubic feet of technically recoverable resources.

A 2009 paper published in Basin Oil and Gas Magazine by Terry Engelder, a professor of geosciences at Pennsylvania State University, predicts a 50 percent chance that the play contains 489 trillion cubic feet of gas.

The Marcellus shale is one of the United States' largest shale gas play, reaching across six states and 95,000 square miles of land, according to NTEL.