Phase I of this project was designed to collect and analyze hydrocarbon gases from three major sources: deep sedimentary basins, abiogenic, and subducted sediments. Results of the analytical scheme have been used to differentiate subduction zone gases from gases of deep sedimentary or mantle origins. One of the major diagnostic tests is the ratio /sup 3/He//sup 4/He, an unequivocal indicator of mantle contribution. Gases were collected and analyzed from the Permian Basin, West Texas, a major deep sedimentary basin, and Iceland, where mantle gases are released into the crust at a spreading ridge. Subduction zone gases were collected in two groups: geothermal gases from volcanic arcs in the Philippines, New Zealand and Alaska, and hydrocarbon production gases from forearc and backarc locations in Taiwan, New Zealand, Alaska, Barbados, Indonesia and the Philippines. Phase II of this project is designed to collect and analyze gases from the western margin of North America, an area of past and present subduction activity, and by applying the differentiation criteria established in Phase I, determine the origin of the gases. 138 refs., 41 figs., 4 tabs.