In 1977, the U.S. Geological Survey, in cooperation with the Energy Research and Development Administration, initiated a geological program? designed to characterize natural gas resources in low-permeability (tight) reservoirs in the Rocky Mountain region. These reservoirs are present from depths of less than 2,000 feet to greater than 19,000 feet. The U.S. Geological Survey is now studying the areas and rock units that have the best resource potential in the region. These are the tight sandstone and siltstone reservoirs of early Tertiary and Late Cretaceous age i:n the Uinta, Piceance, and Greater Green River Basins, and Upper Cretaceous sandstone, siltstone, shale, and marl reservoirs in the northern Great Plains. The. Greater Green River Basin includes. the Green River Basin proper, and the Washakie, Great Divide, and Sand Wash Basins. The gas potential of tight, offshore-marine deposits of the northern Great Plains was first recognized by D. D. Rice. The purpose of the present investigation is to outline the distribution of lml-permeability gas-bearing formations, characterize the reservoirs, assist in improving the recovery technology, and provide a refined estimate of in-place gas resources. The amount of recoverable gas is dependent on economic factors and advancements in recovery technology. A wide variety of geological techniques is being used to resolve resource and recovery technology problems in tight gas sands. These techniques include studies in surface and subsurface stratigraphy, paleoenvironmental interpretation, geophysical borehole logging, computer processing of well history and geologic data, lineament analysis using earth-satellite imagery, scanning electron microscopy, X-ray diffraction and fluorescence, reservoir-rock petrography, pore-throat studies, core analysis, micropaleontology, organic geochemistry, thermal-maturation studies, borehole-gravimeter logging, subsurface-pressure mapping and hydrodynamic analysis.