The composition of ketones from the fraction of weakly polar compounds isolated from crude oils in Jurassic sediments south of the Western Siberian oil-and-gas province has been studied. It has been found that aliphatic ketones are represented by the homological series of n-alkan-2-ones and the isoprenoid ketone 6,10,14-trimethylpentadecan-2-one. Among aromatic ketones, fluorenone, benzofluorenones, dibenzo- and/or naphthofluorenones, and their C(1)-C(4) homologues have been identified.