The Energy Information Administration has been estimating that the Marcellus shale located in the mid-Atlantic states might hold as much 410 trillion cubic feet of natural gas. The U.S. Geological Survey has just released its new estimate—84 trillion cubic feet—that's 80 percent less than the EIA estimate. However, that's up considerably over the agency's earlier estimate. As the USGS press release notes:
These gas estimates are significantly more than the last USGS assessment of the Marcellus Shale in the Appalachian Basin in 2002, which estimated a mean of about 2 trillion cubic feet of gas (TCF) and 0.01 billion barrels of natural gas liquids.
The increase in undiscovered, technically recoverable resource is due to new geologic information and engineering data, as technological developments in producing unconventional resources have been significant in the last decade. This Marcellus Shale estimate is of unconventional (or continuous-type) gas resources.
The EIA has estimated that total U.S. natural gas reserves at 2,600 trillion cubic feet which, if true, implies that there is about 110-year supply of gas at the current rate of 23 trillion cubic feet annually. The new USGS figures cut the estimated reserves to just under 2,300 trillion cubic feet, which roughly suggests an 98-year supply of gas. The EIA is adjusting its Marcellus shale figures in line with the new USGS estimates. This is still far away from "peak natural gas."