Preliminary investigations of a sequence of Upper Cretaceous and Lower Tertiary rocks in the Pacific Creek area of the northeastern Green River Basin show that studies of organic maturation, subsurface temperature, and formation pressure may help define prospective gas-saturated intervals and delineate areas of maximum gas resource potential. At about 11,600 ft (3,500 m), near the base of the Upper Cretaceous Lance Formation, the top of significantly high overpressure has been identified. Drillstem test data indicate that the pressure gradient is as high as 0.84 psi/ft (19.0 KPa/m). The development of overpressure may involve several processes; however, interpretation of the available information indicates that the active generation of large amounts of wet gas is one of the more important processes. A vertical profile of organic maturation, determined by vitrinite reflectance and color alteration of organic material, shows that the top of overpressure and beginning phase of wet-gas generation occurs within, but well below the top of, the "oil window." The present minimum temperature at . 0 0 the top of overpressure is at least 190 F (88 C). This temperature was determined from uncorrected bottom-hole temperatures recorded during logging of wells drilled in the area. The preservation of abnormally high pressures is probably due to presently active generation of gas in a thick interval of discontinuous, very low-permeability shales, siltstones, and sandstones.