The permeance of a 50 mu m thick PdAg (25 wt.% of silver) tubular membrane towards hydrogen was evaluated for hydrogen feed streams or binary mixtures of industrial relevance, namely of H-2/CO or H-2/CO2. It was proposed a rearrangement of the Sieverts-Langmuir (SL) equation to account for the inhibition effect on the membrane permeance towards H-2 due to the presence of CO or CO2. Such modification is based on the average partial pressure of CO or CO2 and the logarithm-mean driving-force to account for concentration gradients along the axial length of the tubular membrane. Comparison with the original SL equation evidenced relative deviations < 10.7%. The experimental data showed good agreement with the SL model. It was found that carbon monoxide has a much stronger inhibition effect on hydrogen permeation than carbon dioxide. Considering the values obtained for the adsorption enthalpy of each gas, it was concluded that both CO and CO2 adsorb physically on the membrane surface. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.