The performance and durability for Ni-YSZ and Ni-ScSZ anodes of solid oxide fuel cells were compared between internal steam and CO2 reforming of methane in the carbon deposition conditions. With a supply of H-2-CO-CO2 mixtures to the anode, the polarization resistance increased with a rise in CO concentrations at 1023 K because of the difficulty of electrochemical oxidation of carbon monoxide. Carbon was produced by the disproportionation of carbon monoxide in CO-CO2 mixture (CO:CO2 = 95:5) at 1023 K, which led to low performance and much degradation of the cells. In comparison between steam and CO2 reforming of methane, the performance and durability in a gaseous mixture at H2O/CH4 = 0.5 were better than that at CO2/CH4 = 0.5. The durability of the Ni-ScSZ anode was superior to that of the Ni-YSZ anode at 1273 K. Amorphous carbon covered the Ni-YSZ anode surface after power generation, which deactivated the nickel catalyst and inhibited gas diffusion. However, crystalline graphite with a rod morphology was grown on the Ni-ScSZ anode, which affected the catalytic activity less than amorphous carbon. The crystallinity and morphology of deposited carbon are important in determining the performance and durability of the cells at low H2O/CH4 and CO2/CH4 ratios. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3435320] All rights reserved.