The methanol steam-reforming reaction to produce synthesis gas has been studied theoretically. A mathematical model has been formulated for a traditional reactor and then applied to a palladium membrane reactor in which the hydrogen production is increased by removing the hydrogen produced from the reaction mixture through a highly selective (100%) palladium-based membrane. In agreement with the literature, the results show that it is possible to obtain both higher conversions of methanol and higher hydrogen selectivities compared to those obtained in a traditional reactor operating at the same experimental conditions. The theoretical analysis provides a set of parameters that permit one to maximize the (pure) hydrogen production and/ or methanol conversion if adopted in an experimental device.