An investigation has been made of the content and molecular composition of porphyrins of crude oils of Carboniferous and Devonian deposits in different areas of the Volga-Urals oil-and gas-bearing province. The data obtained have been analysed by the main components method using two modifications based on an analysis of correlation and covariation matrices. It is shown that the crude oils investigated can be divided into three groups differing in the set of parameters of the molecular composition and in the quantitative content of metalloporphyrins.