A detailed model is presented for the analysis of temperature, species concentration, and current density profiles as well as the efficiency and power density of a planar solid oxide fuel cell at direct internal reforming condition. The model describes the interactions of mass transport, heat transport, heterogeneous chemistry, and electrochemistry. The heterogeneous chemistry model for the catalytic reactions in the anode structure uses a multi-step reaction mechanism for the steam reforming of methane on Ni based catalysts. The porous media transport is modeled using the Dusty Gas Model, and electrochemistry is modeled using a modified Butler-Volmer setting assuming hydrogen as the only electrochemically active species. The impact of flow rate, anode thickness, and catalyst loading on power density and efficiency is discussed for isothermal and adiabatic operating conditions. © The Electrochemical Society.