A La0.6Sr0.4Fe0.8Co0.2O3-Ce0.8Gd0.2O1.9(LSFCO-CGO) composite anode material was investigated for the direct electrochemical oxidation of methane in intermediate temperature solid oxide fuel cells (IT-SOFCs). A maximum power density of 0.17 Wcm(-2) at 800 C was obtained with a methane-fed ceria electrolyte-supported SOFC. A progressive increase of performance was recorded during 140 h operation with dry methane. The anode did not show any structure degradation after the electrochemical testing. Furthermore. no formation of carbon deposits was detected by electron microscopy and elemental analysis. Alternatively. this perovskite material showed significant chemical and structural modifications after high temperature treatment in a dry methane stream in a packed-bed reactor. It is derived that the continuous supply of mobile oxygen anions from the electrolyte to the LSFCO anode, promoted by the mixed conductivity of CGO electrolyte at 800 C. stabilises the perovskite structure near the surface under SOFC operation and open circuit conditions. (c) 2004 Elsevier B.V. All rights reserved.