A strictly anaerobic, moderately halophilic, Gram-negative, non-motile rod-shaped bacterium was isolated from an oil-well head sample of an offshore Congolese oil field. The strain, designated SEBR 4224T (T=type strain), grew optimally at 42°C and pH 7.0 in a complex medium containing 10% NaCl with a generation time of 2.5 h. Strain SEBR 4224T grew on a range of carbohydrates including fructose, galactose, D-glucose, maltose, D-mannose, D-ribose, sucrose, and trehalose. Yeast extract and/or bio-Trypcase was required for growth on carbohydrates and could not be replaced with amino acids and/or vitamins. The end-products from glucose fermentation were acetate, H2, and CO2. Thiosulfate and elemental sulfur were used as electron acceptors. Thiosulfate improved carbohydrate utilization and biomass yields. The G+C content of the isolate was 34 mol%. Ribosomal 16S rRNA sequence analysis showed that strain SEBR 4224T is a new member of the genus Haloanaerobium. The lack of DNA homology with H. acetoethylicum, its closest relative, as determined by DNA-DNA hybridization supports the designation of strain SEBR 4224T as a new species, Haloanaerobium congolense sp. nov. The type strain is SEBR 4224T (=DSM 11287)