An examination is made of the results of investigations over many years (by means of chromate-mass spectrometry) of the composition and quantitative distribution of biomarkers in 400 crude oils of the main oil fields of Russia: West Siberian, East Siberian, Timan-Pechora, Volga-Urals, Ciscaucasia and the Far East. Hydrocarbon biomarkers have been used to assess the most important geochemical indices of the origin and subsequent changes of crude oils in different fields and stratigraphic levels. These indices include the composition of the initial organic matter (OM), the lithofacial conditions of its conversion, the microbiological processing of the OM in diagenesis, the degree of catagenetic maturation of crude oils, the degree of biodegradation of crude oils in formations and others.