n-Alkanes with an odd number of carbon atoms in the molecule and respective unsaturated even-chain fatty n-acids have been found in native biomass of Arthrobacter sp. RV and Pseudomonas aeruginosa RM hemoorganoheterotrophic bacteria. In addition, C-8 and C-10 n-alkanes with an even number of carbon atoms in a much lower concentration compared with odd-numbered alkanes have been found within native biomass of the bacteria under investigation. Both strains have synthesized an unsaturated irregular isoprenane, squalene (2,6,10,15,19,23-hexamethyltetracosa-2,6,10,14,18,22-hexaene). It has been supposed that the prevalence of odd-over even-carbon-number alkanes in low-maturity oils is due to not only high-temperature decarboxylation of the relevant acids with an even number of carbon atoms, but also bacterial synthesis.