The mathematical simulation of a planar solid oxide fuel cell (SOFC) is presented. The model accounts for three-dimensional and time-dependent effects. Internal methane-steam reforming and recycling of the anode gas are also considered. The effects of different flow manifolding, i.e., cross-, co-, or counter-flow are discussed. After a short description of the mathematical procedure, computational results are presented. In particular the distribution of the gases, of the current density and of the solid structure temperature across the cell are shown. Furthermore the effects of different flow manifolding, of radiation from the outer stack surface to the surroundings and of anode gas recycling on the operating conditions of the stack are considered. The response of the cell voltage to a load change is also discussed.