Steam reforming of methane, mainly to hydrogen and carbon dioxide, proceeds over nickel catalysts at 800 K in an equilibrium-shift reactor with a thin palladium membrane 11 mu m-thick supported on a stainless steel porous metal filter. The methane conversion greatly exceeds its equilibrium conversion due to the hydrogen separation with the membrane. The catalytic activity affects the conversion much more than in the cases using an equilibrium reactor. The conversion in the membrane reactor decreases with an increase in the space velocity of the reaction mixture, mainly because of a decrease in the hydrogen separation ratio (rate of hydrogen separation/total production rate of hydrogen). The rate of hydrogen separation depends basically on the hydrogen permeability of the membrane, but an active catalyst also increases the rate; that is, the hydrogen production rate depends on the catalytic activity. Thus, the higher rate causes the higher partial pressure of hydrogen in the reactor, while the hydrogen flux through the membrane depends on the pressure. (c) 2005 Elsevier B.V. All rights reserved.