In this study, the ability of a Pd-Ag membrane reactor of producing ultrapure hydrogen via oxidative steam reforming of ethanol has been evaluated. A self supported Pd-Ag tube of wall thickness 60 mu m has been filled with a commercial Pt-based catalyst and assembled into a membrane module in a finger-like configuration. In order to evaluate the hydrogen yield behavior under different operating conditions, experimental tests have been performed at temperatures of 400 and 450 degrees C and pressures of 150 and 200 kPa. The oxidative steam reforming of ethanol has been carried out by feeding the membrane reactor with a gas stream containing a dilute water-ethanol mixture and air. Different water/ethanol feed flow rates (5, 10,15 g h(-1)), several water/ethanol (4, 10, 13) and oxygen/ethanol (0.3, 0.5, 0.7) feed molar ratios have been tested. The results pointed out that the highest hydrogen yield (moles of permeated hydrogen per mole of ethanol fed) corresponding to almost 4.1 has been attained at 450 degrees C and 200 kPa of lumen pressure by using a water/ethanol/oxygen feed molar ratio of 10/1/0.5. The results of these tests have been compared with those reported for the ethanol steam reforming in a Pd-Ag membrane reactor filled with the same Pt-based catalyst. This comparison has shown a positive effect on the hydrogen yield of small oxygen addition in the feed stream. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.