Composite solid oxide fuel cell (SOFC) anodes consisting of LaSr2Fe2CrO3-delta (LSFeCr) and Gd0.1Ce0.9O2-delta (GDC) were evaluated during operation on H-2, H2O-Ar-H-2, CO, and CO-H-2 mixtures. Impedance spectroscopy studies showed three different electrode processes that varied in importance with temperature and fuel composition. The primary impedance response peaked at similar to 2 Hz and followed a similar dependence on H-2 partial pressure in both H-2-H2O-Ar and H-2-CO mixtures. The total anode polarization resistance at 800 degrees C increased by a factor of similar to 2 on going from pure H-2 fuel to pure CO. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.032302jes] All rights reserved.