Chromato-mass spectrometry has been used to study C-10-C-13 adamantane hydrocarbons in crude oils of different genesis. It has been shown that adamantanes are present both in young and in ancient crude oils of marine and continental genesis, and in mature and immature crude oils generated both by argillaceous and by carbonate rock masses, It has been found that adamantanes are present in crude oils in far-from-equilibrium ratios, Here the concentration of more stable isomers of methyladamantanes falls with increasing molecular weight, The relative concentration distribution of adamantanes can be used as a criterion of the genetic affiliation of crude oils. In crude oils generated in carbonate deposits, the concentration of cis-1,4-dimethyladamantane and cis-1,3,4-trimethyladamantane is appreciably higher than in crude oils generated in argillaceous deposits. A comparative analysis of the distribution of adamantanes and steranes in crude oils has been carried out.