Abstract: With the help of gas chromatography/mass spectrometry, the authers identified a novel homologue with m/z 252+14n (n=0—3) in aromatic fraction of marine source rocks from Mesozoic to Paleozoic. They belong to alkyl-substituted benzofluoranthene and benzo(e)pyrene, compared with the reference. The distribution of last four peaks in m/z 266 mass chromatogram is similar to that of methyl phenanthrene isomers (m/z 192). They are identified as methyl benzo(e)-pyrene.