Three separate emplacement concepts could explain the occurrence of gas at extreme depths: abiogenesis (a primordial, nonbiologic origin source,5409 ); subducted, organic-origin gas (involving the deep, tectonic subduction emplacement of hydrocarbon-generating ocean sediments,5409 ); and deep sedimentary basin gas (the more conventional emplacement of sedimentary rocks by deep downwarping of the Earth's crust). Of these concepts, Deep Source Gas research focuses on the subducted, organic-origin concept. The purpose of Deep Source Gas research is to verify natural gas arising from depths in excess of 30,000 feet, to relate these occurrences to conceptual models, to define the limits of target areas, to quantify the resource, and to determine the significance of the gas to the nation's reserves. The research emphasizes an Earth science study (geology, geochemistry, and geophysics) of the Cordilleran Geologic Province of western North America. This area is considered a prospective source largely because of known and suspected plate tectonic structures and their youthful emplacement, which increase the likelihood of a timely entrapment of deep-source generated hydrocarbons. Detailed geochemical studies indicate that the deep-source-gas generating capacity of the Aleutian Trench area of southern Alaska is high. Furthermore, geophysical studies show that an apparent fossil subduction zone exists in western Washington. This zone appears to have very thick sedimentary rock units, the existence of which will be evaluated through a more detailed seismic study and possibly through drilling activities. Structural observations made in the northern Brooks Range and central Alaskan Range indicate that overthrusting and compressional features may serve as large-scale target areas for deep source gas generation and occurrence. 12 figures, 2 tables.