The distribution of bicyclic sesquiterpanes in crude oils was studied to assess the applicability of the sesquiterpane ratios as maturity parameters. GC–MS analysis was conducted on ten oil samples that were generated in Miocene-Paleogene deposits located within the Kamchatka Peninsula and southeast Chukotka, the Russian Far East. During catagenesis, there is a shift in the distribution of sesquiterpanes with increasing thermal maturity, e.g., a decrease of the relative content of C16 homodrimanes towards an increase of C15 drimanes and C14 sesquiterpanes. New maturity indices, based on sesquiterpanes, correlate well with commonly used maturity indicators, such as a methylphenanthrene index (MPI-1) and a methyldibenzothiophene ratio (MDR) (the R2 value greater than 0.746). Since C14 sesquiterpanes can arise as a product of thermolysis of higher homologues or may be derived from other organic sources, it is not included in one of the new indices.