An experimental campaign has been carried out in order to assess the performance of a two-step membrane process in terms of hydrogen production by methane auto-thermal reforming. A reformer operating at high temperature (700 degrees C) has been coupled with a module consisting of an array of 19 Pd-Ag membranes (length 250 mm, diameter 10 mm and wall thickness 0.150 mm) operating at 300-400 degrees C. The hydrogen produced in the reformer has been selectively separated through the membrane tubes. The capability of the whole system to produce pure hydrogen has been investigated by varying the operating parameters: reformer temperature 580-700 degrees C, reaction pressure 100-500 kPa, water/methane feed molar ratio from 1.5/1 to 4.5/1 and methane feed flow rate in the range 4.47 x 10(-4) 1.11 x 10(-3) mol s(-1). Auto-thermal conditions have been studied by adding air in order to provide oxygen/methane feed molar ratio of 0111, 0.33/1, 0.5/1. A maximum pure hydrogen flow rate of 1.65 x 10(-3) mol s(-1) has been collected in the membrane module shell with a reformer temperature of about 700 degrees C, membrane module temperature of 400 degrees C, reaction (lumen) pressure of 350 kPa, feed molar ratio methane/water/oxygen of 1/3/0.333 and methane feed flow rate of 1.11 x 10(-3) mol s(-1). Under these conditions the hydrogen yield measured has been 1.48. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.