Low permeability gas reservoirs ("tight gas sands") are abundant in the U.S. Economic recovery o f the gas in these formations requires reservoir simulation, usually massive hydraulic fracturing. Significant investigations of tight gas sands by the National Petroleum Council (NPC), Lewin and Associates, and the Gas Research Institute (GRI)* have agreed that, although some formations can be profitably produced with existing technology, improved reservoir diagnostic and stimulation techniques are required to realize the full potential of the resource.