Naturally Adsorbed Gas Survey (NAGS) – Discovers anomalies in the adsorbed gas content of rock samples collected just below the soil level indicative of hydrocarbon prospectivity. NAGS is based on the concept of the gas field of the Earth, a natural flux of gases composed of all of the light homologs of methane as well as other inorganic gases, described as “the background gas field”. As these gases ascend to the surface and interact with hydrocarbon-saturated formations, they undergo alteration in several ways (mechanically, physically, and chemically), and the resulting anomalies in the distribution of gases become manifest at the surface.  Such anomalies, which are a computational result of the analysis of adsorbed gases in rock samples near the surface, only occur when hydrocarbon deposits are present in the subsurface. These anomalies are relational constructs developed in the NAGS model and appear as ring-shaped and crest-and-ring-shaped structures present on the Earth’s surface in terms of the distribution of gas components, various gas proportions, ratios, contrast curves, etc. Contrary to other gas-geochemical technologies that profile subsoil atmosphere and hydrosphere gases (which are highly mobile and not informative), NAGS performs studies of gases firmly enclosed in rock material and stable at surface temperature and pressure. Known as “adsorbed gases”, they accumulate in rocks during the course of migration of gas-saturated fluids at the maturation stage of regional geology. Hence, their characteristics are significantly more informative in contrast to the free gases of other, well known geochemical studies. NAGS profiles gas-concentration anomalies as well as changes in the surface composition of gases. Contrary to the traditional view that surface geochemical anomalies are strictly a result of the migration of hydrocarbon gases from their source deposits, NAGS also accounts for the diffusion process (change in the gas field).