Measurements in a membrane methane reformer packed with catalytic (Pt(3)Ni(10)/CeO2) foams and equipped with a 175 cm(2) Pd membrane showed that high conversion and high hydrogen recovery can be achieved with sweep flow and high pressures (over 90% conversion and over 80% H-2 recovery at 525 degrees C for 0.25 NL/min CH4 feed flow). Increasing pressure above 10 bar does not lead to higher fluxes due to stronger permeance inhibition. A mathematical model predicts the reactor's performance well in terms of axial temperature profile, exit compositions and permeate flow, when membrane permeance is calibrated with experimental results. However this value is significantly lower (by 80%) than values measured in pure H-2 in the absence of reaction. This apparent permeance inhibition is attributed to coadsorbates, although the only strong inhibitor in these conditions is thought to be CO, and its concentration (<1%) cannot justify this strong inhibition. We suggest a mechanistic explanation for this. Concentration polarization effects are not negligible but a 1-D model solution, using an approximation of this effect, shows it cannot account for this large inhibition. (C) 2014 Elsevier B.V. All rights reserved.