From K.B. Battaglini of GT Houston:

The Marcellus Shale contains about 84 trillion cubic feet of recoverable natural gas, and 3.4 billion barrels of recoverable natural gas liquids, according to a just-released assessment by USGS of geological and engineering data.  These estimates are significantly more than the last USGS assessment in 2002, which estimated 2 trillion cubic feet of natural gas and .01 billion barrels of natural gas liquids. 

The new volumetric assessment must be tempered by legal and technical accessibility issues.  In other words, it is not likely that all of the recoverable gas will be recovered.

In reporting on this development, the New York Times slanted the results by proclaiming in a headline that "Geologists Sharply Cut Estimate of Shale Gas."  But the USGS did not cut its 2002 estimate, but rather increased it.  Instead, the Times compared the USGS’s volumetric assessment with a prior estimate made by the Energy Information Administration of 410 trillion cubic feet of natural gas.  Upon learning of the just-released assessment by USGS, the EIA downgraded its prior estimate, saying "we consider the USGS to be the experts in this matter" and "they’re geologists and we’re not."  So, rather than proclaiming that "Geologists" had cut their estimate, the Times headline should have stated that the "EIA downgraded its estimate based upon a geological assessment."