The data, however, tell a very different story. Between the demonstrable gas reserves, and the potential resources blared in the headlines, lies an enormous gulf of uncertainty.
The claim of a 100-year supply originated with a report released in April 2011 by the Potential Gas Committee, an organization of petroleum engineers and geoscientists...Its website consists of a single press release announcing the April report, with a link to a brief summary slide deck. A more detailed slide deck issued by the committee presents some optimistic estimates of potential resources, including a "future gas supply" estimate of 2,170 trillion cubic feet (tcf). At the 2010 rate of American consumption—about 24 tcf per year—that would be a 95-year supply of gas, which apparently has been rounded up to 100 years.
But what is that estimate based upon?
Those details haven’t been made freely available to the public, but their summary breaks it down as follows here and in the graph below: 273 tcf are "proved reserves," meaning that it is believed to exist, and to be commercially producible at a 10 percent discount rate. That conforms with the data of the U.S. Energy Information Administration. An additional 536.6 tcf are classified as "probable" from existing fields, meaning that they have some expectation that the gas exists in known formations, but it has not been proven to exist and is not certain to be technically recoverable. An additional 687.7 tcf is "possible" from new fields, meaning that the gas might exist in new fields that have not yet been discovered. A further 518.3 tcf are "speculative," which means exactly that. A final 176 tcf are claimed for coalbed gas, which is gas trapped in coal formations. (Note: The PGC reports the total for probable, possible, and speculative coalbed gas as 158.6 tcf, but adding up their numbers for each category, we find the correct total is 157.7 tcf. We haven't been able to reach the PGC to discuss the discrepancy. Adding the 18.6 tcf of proved coalbed gas reserves reported by the EIA in 2009—the most recent data it offers—to the 157.7 gives a total of 176.3 tcf for all categories of coalbed gas.
By the same logic, you can claim to be a multibillionaire, including all your "probable, possible, and speculative resources."
Assuming that the United States continues to use about 24 tcf per annum, then, only an 11-year supply of natural gas is certain. The other 89 years' worth has not yet been shown to exist or to be recoverable.
Even that comparably modest estimate of 11 years’ supply may be optimistic. Those 273 tcf are located in reserves that are undrilled, but are adjacent to drilled tracts where gas has been produced. Due to large lateral differences in the geology of shale plays, production can vary considerably from adjacent wells...Please read more from: http://www.slate.com/articles/health_and_science/future_tense/2011/12/is_there_really_100_years_worth_of_natural_gas_beneath_the_united_states_.html