In the present work, the effect of hydrogen removal on carbon formation in a membrane reactor (with nickel supported catalyst) for steam and CO2 methane reforming is analyzed. The steady-state operation of the membrane reactor is described by means of a one-dimensional, heterogeneous, non-isothermal mathematical model. The carbon formation is kinetically evaluated through expressions reported in the literature. Higher CO, contents in the feed stream or operating temperatures increase the risk of carbon formation in both, the membrane and conventional fixed bed reactors. Moreover, for a given feed composition and tube-wall temperature profile, the tendency to carbon deposition is promoted by hydrogen removal and increases as the percentage of hydrogen removed is augmented (for example, by a diminution of the Pd membrane thickness). The proposed model is a useful tool to predict the position where carbon formation is expected in the conventional and membrane reactors for methane reforming, not only along the catalyst tube but also within the Ni particle. (c) 2007 Elsevier B.V. All rights reserved.