The methane steam reforming reaction has been investigated from a modelling viewpoint, considering the effect of different parameters on methane conversion. For example, considering the influence of the lumen pressure on methane conversion at constant temperature, it has been found that increasing this parameter, equilibrium methane conversion increases for the membrane reactor, while it decreases for the traditional one. Moreover, in a realistic membrane reactor (i.e. considering a simulation performed using kinetic expressions), the behaviour of methane conversion versus lumen pressure at various temperatures shows a minimum value, depending on the membrane thickness, on the reactor length and on the temperature. (C) 2003 International Association for Hydrogen Energy. Published Elsevier Ltd. All rights reserved.