A dense tubular Pd-Ag membrane reactor was used to carry out the methanol steam reforming reaction for producing a CO-free hydrogen stream. A Cu/Zn/Mg-based catalyst was packed in the lumen side of the membrane reactor and the experimental tests were performed at a reaction temperature of 300 degrees C and at a H2O/methanol feed molar ratio of 3/1 The effects of the different flow configurations as well a the sweep factor and the reaction pressure were analysed. Experimental results in terms of CO-free hydrogen recovery, hydrogen yield, CO-free hydrogen yield and hydrogen selectivity are presented. Moreover, a comparison between the performances of the membrane reactor and a traditional reactor working at the same operative conditions is proposed and discussed. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.