Roughly, one trillion cubic feet of natural gas is enough to heat 15 million homes for one year.

Jim Coleman, director of the USGS eastern energy resources science center, said he and his staff are still trying to figure out the differences between their report and the DOE analysis.

Initially, Coleman said that the DOE report counted both resources that were already being drilled or producing gas and those that are not yet being drilled or in production, while the USGS study examined only gas resources considered "undiscovered" resources, or those not yet being drilled or in production. This difference is methodology could explain part of the conflicting results, Coleman said in a phone interview.

But the DOE report said that agency's analysis specifically said its numbers did not include the undiscovered gas reserves.

"We're trying to get an understanding of what this really means," Coleman said. "I'm not understanding what they counted and how they got their numbers. That's not to say they're wrong, but I just don't understand how they got their numbers."

The conflicting reports come amid pressure from Congress and federal securities regulators about whether some oil and gas companies have inflated the potential of the Marcellus Shale, and questions about how federal agencies come up with their estimates.

A DOE spokesman did not return phone calls or emails seeking comment on the differing study results, but told other media outlets his agency would adopt the USGS numbers.

Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.

CHARLESTON, W.Va. -- Federal officials are scrambling to explain two widely conflicting estimates of the size of the natural gas reserves that drillers might be able to recover from the Marcellus Shale.

A new U.S. Geological Survey, issued Tuesday, concluded the Marcellus -- a formation that stretches from New York to Tennessee -- contains 84 trillion cubic feet of undiscovered, technically recoverable natural gas.

That estimate came in 42 times larger than the 2 trillion cubic feet projected in a USGS report published nearly a decade ago, largely because of technological advances in horizontal drilling and hydraulic fracturing.

But media reports have emphasized that the new USGS estimate is much smaller than a projection published just last month by the U.S. Department of Energy's Energy Information Administration.

The DOE analysis reported that there were 410 trillion cubic feet of natural gas in the Marcellus Shale, a figure that helped fuel continued speculation that drilling in the formation could be an economic powerhouse for West Virginia and other states in the region.

By comparison, total U.S. natural gas production was about 22.6 trillion cubic feet last year. West Virginia produced about 255 billion cubic feet in 2009, the most recent year for which figures were immediately available Thursday. Only 20 billion cubic feet of West Virginia's production came from shale gas wells.

Roughly, one trillion cubic feet of natural gas is enough to heat 15 million homes for one year.

Jim Coleman, director of the USGS eastern energy resources science center, said he and his staff are still trying to figure out the differences between their report and the DOE analysis.

Initially, Coleman said that the DOE report counted both resources that were already being drilled or producing gas and those that are not yet being drilled or in production, while the USGS study examined only gas resources considered "undiscovered" resources, or those not yet being drilled or in production. This difference is methodology could explain part of the conflicting results, Coleman said in a phone interview.

But the DOE report said that agency's analysis specifically said its numbers did not include the undiscovered gas reserves.

"We're trying to get an understanding of what this really means," Coleman said. "I'm not understanding what they counted and how they got their numbers. That's not to say they're wrong, but I just don't understand how they got their numbers."

The conflicting reports come amid pressure from Congress and federal securities regulators about whether some oil and gas companies have inflated the potential of the Marcellus Shale, and questions about how federal agencies come up with their estimates.

A DOE spokesman did not return phone calls or emails seeking comment on the differing study results, but told other media outlets his agency would adopt the USGS numbers.

Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.