This paper presents a performance analysis of a planar SOFC (solid oxide fuel cell) with proton-conducting electrolyte (SOFC-H+). The SOFC-H+ is fueled by methane and operated under direct internal reforming and isothermal conditions. A one-dimensional steady-state model coupled with a detailed electrochemical model is employed to investigate the distribution of gas composition within fuel and air channels and all the electrochemical-related variables. The current voltage characteristics of SOFC-H+ are analyzed and the result shows that the operation of SOFC-H+ at 0.7 V gives a good compromise on power density and fuel utilization. However, high CO content at fuel channel is observed at this condition and this may hinder the SOFC-H+ performance by reducing catalyst activity. The effect of key cell operating parameters, i.e., steam to carbon ratio, temperature, pressure, and water content in oxidant, on the performance of SOFC-H+ and the content of CO is also presented in this study. (C) 2009 Elsevier Ltd. All rights reserved.