A 3D simulation tool for solid oxide fuel cells is presented. The aim of this work is to predict current density, flow, temperature and concentration fields in order to compare and optimize repeat element geometry for a whole stack. A commercial CFD tool was used, solving mass, momentum and energy equations; whereas chemical kinetic equations are computed from external sub-routines. A steady-state case is presented, fed with hydrogen. The flow is laminar for both air and fuel. Radiative heat transfer is taken into account between inner surfaces. On boundaries, convective and radiative heat transfers are assumed at external surfaces between repeat element and oven. Due to the large range of dimensions (cells: 300 mum thick, gas channels: 1 mm height, whole cell: 80 mm x 80 mm) a fine mesh was needed. Data for conductivities and kinetics were estimated from experiments performed in-house. Simulation results are presented and compared to real repeat element test measurements for the current-potential characteristics. (C) 2004 Elsevier B.V. All rights reserved.