This paper describes the performance of composite La0.8Sr0.2Cr0.82Ru0.18O3-delta-Gd0.1Ce0.9O2 anodes operated in varied H2O-H-2, CO-CO2. and H2O-H-2-CO-CO2 fuel mixtures. Impedance spectroscopy studies in both H2O-H-2 and CO-CO2 showed two main impedance responses that were thermally activated and exhibited power law variation with gas partial pressures. The polarization resistances in CO-CO2 mixtures were larger than in H-2-H2O mixtures with the same partial pressure ratios. Polarization resistances for surrogate coal syngas H2O-H-2-CO-CO2 fuel mixtures were higher than for H2O-H-2-Ar mixtures with the same H-2 and H2O partial pressures, indicating that CO or CO2 interfered with the H2 oxidation reaction. (C) 2011 Elsevier B.V. All rights reserved.