A disc-shaped methanogenic bacterium designated strain SEBR 4847T (T=type strain) was isolated from a sample collected from an African offshore oil field. Strain SEBR 4847T was non-motile, had a G+C content of 50 mol% and produced methane from H2+CO2, formate, and CO2+propanol. Strain SEBR 4847T grew optimally at 37°C; no growth was observed at 25°C or 45°C. It grew in the presence of up to 50 g/l NaCl; 10–30 g/l was required for optimal growth. The optimum pH for growth was 7.0. Doubling time was about 10 h under optimal conditions. Based on 16S rRNA sequence analysis, the isolate was identified as a new species of the genus Methanoplanus and designated Methanoplanus petrolearius sp. nov. The type strain is SEBR 4847T (=OCM 486).