Since the early 1960s the Potential Gas Committee (PGC) has been preparing periodic estimates of the potential resources of natural gas in the United States. The committee operates independently from any other group, either industry or government, and its published estimates represent the consensus of the working members who are organized into committees, one for each major producing area of the United States. Over the years, many people have participated. Total United States natural gas resources consist of cumulative past production plus present proved reserves plus undiscovered potential resources. The PGC estimates undiscovered potential resources only. With time the various components of the total recoverable resource should reflect a gradual shift from the potential category through proved reserves into production. Indeed, as the cumulative production in the United States has increased and the proved reserves have gradually decreased in recent years, the potential estimated independently by the PGC has changed gradually and the estimate of the total recoverable resource has remained remarkably consistent. Within individual areas the estimate of the undiscovered potential has shifted rather markedly, but the overall picture for the entire country has varied within close limits. Variations in the estimate of potential for individual areas can be attributed to the progress of exploration and the exploration philosophy of committee members.