The performance of an original membrane methane reformer is analyzed by a two-dimensional mathematical model. The reactor is a bundle of four coaxial double tubes inserted in a shell in which a heating fluid flows. The annular region of each tube is the reaction zone, whereas the inner tube is the selective membrane for hydrogen removal. Many simulations have been carried out in order to find a suitable set of values of geometric and operating design variables. The effect of pressure and sweeping gas flow rate at permeation side, of membrane diameter and of axial profile of heat flux supplied to the reactor is analyzed in 81 virtual experiments. Suitable operating conditions are found: over 58% methane conversion can be reached, within a proper membrane temperature range and extra methane consumption for thermal duty. (C) 2007 Elsevier B.V. All rights reserved.