A novel Gram-negative, aerobic and moderately thermophilic bacterium, strain 4BONT, was isolated from a non-water-flooded Australian terrestrial oil reservoir. Cells were non-spore-forming straight rods, which were motile by means of a polar flagellum. The optimum growth conditions were 55 ì pH 6繠and 0絠% NaCl. Strain 4BONT was oxidase- and catalase-positive; it grew on fumarate, pyruvate, succinate, formate, ethanol and yeast extract in the presence of oxygen or nitrate as terminal electron acceptor. Nitrate was reduced to nitrous oxide. The DNA G+C content of the strain was 58綠mol%. The closest phylogenetic relative of strain 4BONT was Hydrogenophilus thermoluteolus (similarity of 91縠%), of the -Proteobacteria. As strain 4BONT is physiologically and phylogenetically different from H. thermoluteolus, it is proposed that it be assigned to a novel species of a novel genus, Petrobacter succinatimandens gen. nov., sp. nov. The type strain is 4BONT (=DSM 15512T=CIP 107790T).