A Process Development Unit (PDU) has been built to test Pd membranes with a capacity of 8.5 N m(3)/hH(2) product, exceeding typical lab scale testing by orders of magnitude. The inhibition effect of water-gas shift (WGS) components on the H-2 permeation was investigated through three Pd membranes of 44 cm long in parallel configuration with the WGS composition: 4.0% CO, 19.2% CO2, 15.4% H2O, 1.2% CH4 and 60.1% H-2 representing the reformate gas from an oxygen-fed autothermal reformer followed by a shift reactor, at near practical operation conditions: 673K. 20-35 bar(a) feed pressure and 30-90 NL/min feed flow rate. The inhibition effect of WGS-components resulted in a H-2 flux decrease of around 20% compared to H-2/N-2 mixtures with the same H-2 concentration, which increased with feed pressure. CO and CO2 both had inhibitive effects on the H-2 permeation. CO was more inhibitive than same amount CO2 but CO2 showed a stronger inhibition effect than CO in the WGS-mixtures due to its 4 times higher amount. The H-2 flux of WGS-mixtures remained unchanged at 673 K in short stability tests. The influence of mass transfer on the H-2 permeation was found to be significant and there was no apparent change in the mass transfer resistance with the variation of feed pressure. (C) 2010 Elsevier B.V. All rights reserved.