The CO inhibition effect on H-2 permeance through commercial Pd-based membranes was analysed by means of permeation measurements at different CO compositions (0-30% molar) and temperatures (593-723 K) with the aim to determine the increase of the membrane area in order to compensate the H-2 flux reduction owing to the CO inhibition effect. The permeance of H-2 fed with carbon monoxide was observed to decrease with respect to the case of pure hydrogen. At 647 K the H-2 permeance of a pure feed of 316 mu mol m(-2) s(-1) Pa-0.5 reduces progressively until 275 mu mol m(-2) s(-1) Pa-0.5 when 15% or more of CO is present in the system, until it reaches a plateau at 20%. The inhibition effect occurring when CO is present in the feed stream reduces with the progressive temperature increase; the reduction of the permeance decreases exponentially by 23% at 593 K and by 3% at 723 K with 10% of CO. The inhibition effect is seen to be reversible. An H-2 flux Profile in a Sieverts' plot shows the effect produced by the increase of the CO composition along the Pd-based membrane length. The H-2 flux profile allows the area of a Pd-based membrane to be evaluated in order to have the same permeate flow rate of H-2 when it is fed with CO or as a pure stream. Moreover, a qualitative comparison between the H-2 flux profiles and a previously proposed model has been carried out. Although studies on the CO inhibition and dilution effects are present in the literature, however, an appropriate evaluation of the H-2 membrane purification unit surface using measurements of permeances of H-2 mixed with CO has until now never been proposed. This information proves important in the design of a hydrogen purification unit. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.