On the basis of data on the occurrence of methane and sulfur in the Earth's interior as well as reactive potential of the alkane–sulfur system, it has been suggested that geosphere degassing might involve the condensative conversion of hydrocarbon fractions of fluids. The condensation effect of sulfur on methane and products of its condensation may be considered as the initial stage of abiogenic oil formation. It has been revealed that the reactivity of the alkane–sulfur system and regularities of its evolution were in good agreement with the characteristics of real oils, such as hydrocarbon-type content, condensation degree, sulfur content, fraction distribution of sulfur and sulfur-containing compounds. Also discovered was a direct relationship among sulfur concentration in oil, scale of oil fields and reserves of oil and gas. The present review deals mainly with contributions published in Russian journals.