Methane steam reforming, with and without added oxygen, was theoretically and experimentally investigated using microporous silica membranes, thus allowing the permeation of hydrogen as well as other gases in reactants and products. A simulation of catalytic membrane reactors was carried out for a cocurrent, isothermal, and plug-flow-type membrane reactor with the selective permeation of hydrogen through microporous membranes. The effect of operating conditions on the conversion of methane and hydrogen production is discussed with the aid of two dimensionless numbers, the Damkohler number (Da) and the permeation number (theta). Methane conversion, X-CH4, has approximately the same dependency on permeation number in terms of the permeability ratios of hydrogen over nitrogen, whereas the purity of hydrogen in the permeate increased with increasing hydrogen selectivity. Catalytic membrane reactors, consisting of a silica microporous layer and a Ni-catalyst layer, were prepared. The permeability ratio of hydrogen over steam, alpha(H-2/H2O), which ranged from 1 to 20, showed a relatively good correlation with that for helium over hydrogen, alpha(He/H-2). Catalytic membrane reactors showing a hydrogen selectivity over nitrogen of 30-100, with hydrogen permeances of 0.5(-3) X 10(-7) mol m(-2) s(-1) Pa-1 were applied to the steam reforming of methane with and without the addition of oxygen. The reaction was carried out at 500degreesC, and the feed and permeate pressure were maintained at 100 and 20 kPa, respectively. Methane conversion, X-CH4, increased up to approximately 0.8 beyond the equilibrium conversion of 0.44 by extracting hydrogen in permeate stream. (C) 2004 American Institute of Chemical Engineers