A thermodynamic tool based on the 'reactor in series method' was used to evaluate the equilibrium conversion of dehydrogenation reactions such as methane steam reforming (MSR) and water gas shift (WGS) in a Pd-based membrane reactor (MR). The permeation equilibrium, expressed by the equality of the H-2 partial pressure on reaction and permeate sides, was imposed as the further constrain for MR. The equilibrium conversion shift is an increasing function of the sweep factor, which is an index of the extractive capacity of the membrane system. The equilibrium conversion of a MR was analysed as a function of temperature and pressure. It shows the same trend vs. temperature for MR and traditional reactor (TR). On the contrary, pressure play a very important role because it has a different influence on the equilibrium of MR with respect to a TR. In particular, the positive effect on thermodynamic conversion was shown also for the MSR reaction characterised by Deltav > 0. (C) 2003 Elsevier Science B.V. All rights reserved.