How Much Natural Gas Does the Marcellus Really Hold?

At the Pittsburgh Tribune-Review (via MDN):

...Industry critics have accused drilling companies and their allies in the research community of trumping up projections to inflate stock prices and for personal gain.
Federal geologists explained their methodology by phone, saying they were only assessing resources yet to be discovered and not anything currently being tapped. Scientist and project chief Christopher Schenk declined to explain other major differences between estimates from the survey and the private sector, saying his team's assessment stood on its own.
"When we put that out, it's not in any context of anything," Schenk said. "You have to know the methodology used, who funded it and why that assessment was put out. We do not say other assessments are wrong. We say they've been done for other purposes."
Several conference participants, including petroleum engineers, geologists and government officials, criticized federal agencies for not doing more to clear up confusion about the numbers. The conference organizer, Penn State geosciences professor Terry Engelder, conceived the summit, which had about 20 participants, as a way to resolve differences between estimates from federal researchers and academic and private researchers.
Engelder in 2009 projected the Marcellus could produce 489 trillion cubic feet of gas. His paper was not peer-reviewed, but other researchers, working with data from well production and test data from other shale plays, have reaffirmed his estimates, he said.
ICF, an industry consultant based in suburban Washington, estimated a range of 460 to 698 trillion cubic feet of gas, according to a presentation from company vice president Harry Vidas. ICF used maps from five major gas producers, analyzed historical data and modeled well potential...