A rigorous mathematical model is used for the simulation of steam and CO2 reforming in fluidized bed membrane reactors. A well-mixed catalyst pattern is implemented to couple the reactions. It has been shown that the combined effect of the membrane and reaction coupling provides exciting opportunities to overcome the equilibrium conversion limits and to achieve complete conversion of methane. The results indicate that the complete conversion of methane at low temperature is possible. Optimal conditions are observed to exist and an effective reactor length criterion is used to evaluate the reactor performance. The influence of some key parameters on the optimal conditions and the reactor such as temperature, pressure, steam to carbon ratio and membrane thickness have been investigated. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.