Anode-supported planar solid oxide fuel cells (SOFCs) were fabricated by a single-step cofiring process. It comprised of a porous Ni + yttria-stabilized zirconia (YSZ) anode support, a porous and fine-grained Ni + YSZ anode active layer, a dense YSZ electrolyte, a fine-grained porous Ca-doped LaMnO3 (LCM) + YSZ composite cathode active layer, and a porous LCM cathode current collector layer. The cell was tested between 700 and 800 degrees C with humidified hydrogen (97% H-2 + 3% H2O) as the fuel and air as the oxidant. The measured maximum power densities were 1.42 W/cm(2) at 800 degrees C, 1.20 W/cm(2) at 750 degrees C, and 0.87 W/cm(2) at 700 degrees C. The cell was also tested at 800 degrees C with various compositions of fuel and oxidant, and the cell parameters, which included the area specific ohmic resistance, exchange current densities, and anodic and cathodic limiting current densities, were obtained through polarization modeling. The polarization resistances of the cell were calculated using the cell parameters obtained from modeling, and compared with the corresponding values measured using impedance spectroscopy. The effect of cell operating conditions on various polarization losses and performance was analyzed in detail using the polarization modeling results. (C) 2008 The Electrochemical Society.