Reduced-temperature solid oxide fuel cells (SOFCs) - with thin Ce0.85Sm0.15O1.925(SDC) electrolytes, thick Ni-SDC anode supports, and composite cathodes containing La0.6Sr0.4Co0.2F0.8O3 (LSCF) and SDC -were fabricated and tested with iso-octane/air fuel mixtures. An additional supported catalyst layer, placed between the fuel stream and the anode, was needed to obtain a stable output power density (e.g. 0.6 W cm(-2) at 590 degrees C) without anode coking. The Ru-CeO2 catalyst produced CO2 and H-2 at temperatures < 350 degrees C, while H-2 and CO became predominant above 500 degrees C. Power densities were substantially less than for the same cells with H-2 fuel (e.g. 1.0 W cm(-2) at 600 degrees C), due to the dilute (20%) hydrogen in the fuel mixture produced by iso-octane partial oxidation. Electrochemical impedance analysis showed a main arc that represented approximate to 60% of the total resistance, and that increased substantially upon switching from hydrogen to iso-octane/air. (c) 2005 Elsevier B.V All rights reserved.