Oscillation of open circuit potential (OCP) and potential is observed for the methane oxidation reaction on (La0.75Sr0.25)(Cr0.5Mn0.5)O-3 (LSCM) and LSCM/YSZ composite electrodes of solid oxide fuel cells (SOFCs) in weakly humidified methane (i.e., 97%CH4/3%H2O). In dry methane (i.e.. 100%CH4), the potential oscillation is reduced significantly. The oscillation behaviour of OCP is also found to be strongly related to the temperature, the microstructure of the composite electrode and the fuel composition. The results indicate that the potential oscillation is thermally activated and is most likely associated with the adsorbed oxygen species on the electrode surface. (C) 2007 Elsevier B.V. All rights reserved.