Two types of solid oxide fuel cells (SOFCs), with thin Ce0.85SM0.15O1.925 (SDC) or 8 mol% Y2O3-stabilized ZrO2 (YSZ) electrolytes, were fabricated and tested with iso-octane/air fuel mixtures. An additional Ru-CeO2 catalyst layer, placed between the fuel stream and the anode, was needed to obtain a stable output power density without anode coking. Thermodynamic analysis and catalysis experiments showed that H-2 and CO were primary reaction products at approximate to 750 degrees C, but that these decreased and H2O and CO2 increased as the operating temperature dropped below approximate to 600 degrees C. Power densities for YSZ cells were 0.7 W cm(-2) at 0.7 V and 790 degrees C, and for SDC cells were 0.6 W cm(-2) at 0.6 V and 590 degrees C. Limiting current behavior was observed due to the relatively low (approximate to 20%) H-2 content in the reformed fuel. (c) 2005 Elsevier B.V. All rights reserved.