Abstract The mission of the Potential Gas Committee (PGC) is the monitoring of undiscovered supplies of natural gas in the United States and periodic publication of its estimates. Potential supply of natural gas is that quantity of natural gas yet to be proved (as the term proved is used by the American Gas Association’s Committee on Natural Gas Reserves) by wells to be drilled under conditions of adequate but reasonable prices and normal improvements in technology. Estimates of potential supply are made by members of 11 Work Committees for 12 areas which may include one or more geologic provinces. The results are published periodically for the guidance of government, the gas industry, and financial institutions. The guidelines for preparing estimates are flexible, and may change with improved technology and greater incentive. For example, undiscovered supplies of natural gas such as those locked in “tight” sandstones in several basins in the Rocky Mountain region will be included in the estimates when technologic and economic feasibility is demonstrated. At this time, drilling depths are limited to 30,000 ft (9,144 m) and water depth to no more than 1,500 ft (457 m). The estimates are defined by decreasing degrees of certainty: “probable,” “possible,” and “speculative.” The probable supplies are closely related to proved reserves and result from extensions to known gas deposits and new-pool discoveries. Possible supplies result from new-field discoveries in formations previously productive in a particular geologic province. Speculative supplies, which are the least certain, may lie in formations not previously productive in a productive province or in a province in which there is no production. Undiscovered supplies do not include proved reserves estimated by the AGA Committee on Natural Gas Reserves. PGC and the AGA Committee are completely separate entities, but communicate through their respective chairmen to avoid duplications. The PGC uses the geologic-volumetric or “attribution” technique developed by Lfewis G. Weeks and others for estimating undiscovered oil, but some refinements have been made in the technique. Estimates are not based on the gross rock volume of each province, but on volume of individual zones producing, condemned, and potential. Estimates of speculative supply are based on character of potential producing sediments and by comparison with productive zones or provinces with similar characteristics. Estimates are checked against historical and statistical data and other pertinent information available to the Work Committees. Obviously, judgment plays an important role in formulating estimates of undiscovered gas supplies. Each member of a Work Committee has a high degree of expertise in the local area to which he is assigned. Workshops for members of one or more Work Committees are held periodically to develop uniformity in estimating techniques and to evaluate continuously the judgment factor. A Special Projects Committee undertakes assignments which may be beneficial to the PGC in making and evaluating its estimates. An Editorial Committee organizes the report for publication. The PGC consists of over 100 individuals, mostly geologists and engineers, from all branches of the gas industry including distribution, production, and pipelines, fcoth interstate and intrastate. In addition, there are observers from the USGS, FPC, EPA, NARUC, AGA, INGA, API, and the Office of Oil and Gas. Important changes are made as a result of consensus, and not by simple majority, and then only after spirited discussion and careful consideration. The Committee is a close-knit, dedicated group of outspoken, rugged individualists. Despite the periodic publication of a wealth of superior, detailed information which is unavailable from any other source, the PGC is not without critics. Perhaps the criticism most commonly made is that the Committee makes no estimate of the rate at which its estimated undiscovered supplies of natural gas can be converted to reserves. The Committee is currently reviewing its methods, format, frequency of publication, possible additions and deletions to its reports, and other aspects of its work to make its efforts more productive and useful.