The term applied to natural gas so difficult and expensive to produce that the sources have been bypassed in favor of more easily obtainable supplies. Such sources are to be found in tight sandstone reservoirs in the western and southwestern states, in certain shales in the appalachian basin, and in geopressurized reservoirs along the gulf coast. Geologists have known of these sources for many years but, because of the low prices for conventional, more cheaply producible conventional gas, the unconventional gas supplies have remained untouched. Also, to get at these marginal sources advances in technology have to be developed, and at great cost.
