A mathematical model of a membrane reactor used for methane steam reforming was de- veloped to simulate and compare the maximum yields and operating conditions in the reactor with that in a conventional fixed bed reactor. The meth- ane steam reforming reaction has been investigated from a modeling viewpoint, considering the effect of different parameters on methane conversion and H2/CO ratio. Results show that the membrane reac- tor presents higher methane conversion yield and can be operated at milder conditions than the fixed bed reactor. Control of the H2/CO ratio is possible in the membrane reactor making the technology more suitable to be used in connection to gas-to-liquid processes (GTL).