Chemical-looping combustion is a promising technology for the combustion of gas or solid fuel with efficient use of energy and inherent separation of CO2, Chemical-looping combustion of methane with calcium sulfate as a novel oxygen carrier was conducted in a laboratory scale fixed bed reactor. The effects of reaction temperature, gas flow rate, sample mass, and particle size on reduction reactions were investigated and an optimum operating condition was determined. The results show that this novel oxygen carrier has a high reduction reactivity and stability in a long-time reduction/oxidation test. The conversions of CH4 increased with a higher temperature, smaller gas flow rate, larger sample mass and smaller particle size. The suitable reaction temperature seems to be around 950 degrees C. Low temperatures lead to a low CH4 conversion, but a significant SO2 formation was observed at a higher temperature. The release Of SO2, CO, H-2 via a series of side reactions, carbon deposition and agglomeration were also discussed. The formation Of SO2, CO, H-2, and carbon can be avoided by optimization of the operating conditions. (C) 2008 Elsevier Ltd. All rights reserved.