A petroleum-degrading bacterium, strain HD-1, was grown anaerobically with CO2 and H-2 as Sole carbon and energy sources, respectively. Electron microscopic observation revealed that many granules were accumulated inside the cell. GC/MS analysis of the cell components showed that the bacterium fixed CO2 and produced alkanes/alkenes with carbon numbers from 14 to 30 besides fatty acids and poly-beta-hydroxyalkanoic acids. By employing HD-1 cell extract, fatty acid and fatty aldehyde were found to be utilized as substrates in the alkane/alkene biosynthetic pathways.