A planar solid oxide fuel cell (SOFC) was fabricated using a tape-cast Ni/yttria-stabilized zirconia (YSZ) anode support, a YSZ thin-film electrolyte, and a composite cathode of YSZ and (La0.85Sr0.14)(0.98)MnO3 (LSM). Using pure hydrogen as the fuel gas, a three-cell stack with a cross-flow design and external manifolds produced peak power densities of 0.85 and 0.41 W/cm(2) at 800 and 700degreesC, respectively. Using wet methane as the fuel gas, the stack produced a peak power density of 0.22 W/cm(2) at 700degreesC. Individual cells in the stack showed identical current-voltage characteristics. Stack lifetime was limited because of degradation of the cells from oxidation products coming from the metallic interconnect used. (C) 2004 The Electrochemical Society. All rights reserved.