This paper investigates a planar anode-supported solid oxide fuel cell (SOFC) with mixed-conducting electrodes. Direct internal methane reforming in the high-temperature cell is included. The numerical model used is three-dimensional, a single computational domain comprising the fuel and air channels and the electrodes-electrolyte assembly. The oxygen ion transport through the electrolyte is mimicked with an algorithm for Fickian diffusion built into the commercial computational package Star-CD. The equations describing transport, chemical and electrochemical processes for mass, momentum, species and energy are solved using Star-CD with in-house developed subroutines. Results for temperature, chemical species and current density distribution for co- and counter-flow configurations are shown and discussed. For co-flow, a sub-cooling effect manifests itself in the methane-rich region near the fuel entrance, while for counter-flow a super-heating effect manifests itself somewhat further downstream, where all the methane is consumed. Effects of varying air inlet conditions are also investigated. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.