The total of probable, possible, and speculative resources of undiscovered recoverable natural gas from conventional reservoirs in Pennsylvania is estimated to be approximately 8.5 tcf. The total undiscovered and potentially recoverable gas resource in unconventional reservoirs may be about 11.1 tcf.

Conventional natural gas resources were estimated in five general stratigraphic "packages," using differing approaches made necessary by the variable character and density of the data available, conditioned by time considerations. These packages and their total of probable, possible, and speculative resources are: Mississippian and Upper Devonian sands, 3.6 tcf; Onondaga/Oriskany and related reservoirs, 1.5 tcf; Lower Silurian Medina Sandstones, 1.8 tcf; Silurian Tuscarora and Cambrian-Ordovician formations, 0.7 tcf; Eastern Overthrust belt, 0.9 tcf.

Unconventional resources are: natural gas in coal beds, 2.7 tcf; Devonian shale gas, 8.4 tcf.

General subdivisions of the estimated conventional resources are 31% probable, 40% possible, and 29% speculative. In contrast, subdivisions of estimated unconventional resources are 11, 24, and 65%, respectively.

Short-term projections demonstrate that production of natural gas in Pennsylvania can be doubled without stress and maintained at that level for several years. Much beyond 10 yr, however, projections become speculations. One can say only that significant quantities of natural gas will be produced in Pennsylvania for many more decades. Whether gas production 50 yr hence will be in greater, equal, or lesser quantities than current production is beyond meaningful prediction.

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