The aim of this work was to assess the potential for bacterial oxidation of hydrogen sulphide as a purification method of sour gas. Using a continuous culture of Chlorobium limicola, high efficiencies of oxidation of both soluble and gaseous sulphide were achieved, with efficiencies for the latter exceeding 95%. Sulphide added as aqueous sodium sulphide was converted to sulphur and sulphate with almost total removal of the initial 100mg S l(-1) within 24 h. Gaseous sulphide was oxidized at an efficiency of 95% (approximately 3 mmol S h(-1) (unit biomass Abs)(-1)) over 1 h runs at a gas flow rate of 60 ml min(-1). With a sulphur recovery system to prevent sulphur accumulation, an efficiency of 70% was maintained. Biological removal of sulphide represents a potentially important biotechnological process, with high potential for viable scale up. Crown Copyright (C) 2007 Published by Elsevier Inc. All rights reserved.