This paper presents a critical review of recent advances in the study of generation, maturation, and migration of petroleum. The different source potentials for generating hydrocarbons depend on the type of kerogen. In addition to the classic types I, II, and III, a residual, oxidized organic matter is also observed, which has no potential for hydrocarbon generation. Coal is widely considered as a potential source for gas, but some coals may generate sizeable amounts of oil as well. The development of routine analytical tools, particularly pyrolysis, makes possible the preparation of geochemical logs that are the basis for screening samples and for interpreting other analyses. Among optical techniques, the major subjects of discussion concern the nature of amorphous organ c matter, which may encompass different chemical types of kerogen, and the applicability of vitrinite reflectance techniques to type I and II kerogens. Following important advances in identification of biological markers in sediments and crude oils, these markers are used for oil-source rock correlation, and proposed for reconstruction of depositional environment and subsequent thermal evolution. Migration of hydrocarbons is now better understood, and the importance of a hydrocarbon-phase migration is widely recognized. Overpressuring of pore fluids is mainly responsible for expulsion of petroleum. Geologic models of basin evolution (subsidence, compaction, thermal history) and geochemical models (hydrocarbon generation and migration) become progressively available. Their integration int a comprehensive model should be one of the major developments in future petroleum exploration.