Despite recent advances in surface and near-surface geochemical methods, there continues to be a need for improved understanding of the scientific basis relating these methods to petroleum deposits. We have reviewed the literature pertinent to the several methods we have used and integrated that information with some 100 man-years of our experience to contribute to that end. Evidence indicates that hydrocarbon microseepage from reservoirs most probably involves buoyant colloidal-size ＇＇microbubbles" of light hydrocarbons (principally methane through the butanes) ascending relatively rapidly through a water-filled network of fractures, joints, and bedding planes. Bacterial consumption of these hydrocarbons creates carbon dioxide and hydrogen sulfide, which may alter sediments, producing detectable modifications in geomorphic, seismic, magnetic, and radiometric properties. We have used combinations of (1) airborne microwave sensing and laboratory analyses of soil gas hydrocarbons, (2) shallow-source aeromagnet ic and soil magnetic susceptibility measurements, (3) aerial and surface gamma-ray measurements, and (4) geomorphology to-find productive oil and gas deposits. Results suggest that using these methods can substantially increase the probability of wildcat success and reduce finding costs in selected geologic settings; however, these surface methods cannot reveal depth, size, or quality of reservoirs, or even if producible hydrocarbons will be found.