A bubbling fluidized bed membrane reactor for steam reforming of methane is mathematically investigated, with the permselective Pd membranes removing hydrogen from the reaction system to enhance the methane conversion. Oxygen fed into the reaction system can decrease the endothermicity of the overall reaction by the combustion of methane, thereby reducing the need of external firing. Operation at low feed steam-carbon ratios is also possible with the steam required for the reforming reaction being provided as a product from the combustion reactions, although problems related to coking also need to be addressed at very low ones. A drop in the reactor temperature at the inlet of the reactor itself due to the high endothermicity and fast kinetics of the steam reforming reactions does not strongly support the idea of a higher feed temperature favoring the reaction conversion. Thereafter, in situ generation of heat by the combustion reactions is a more effective means to give better reactor performance, and a higher feed temperature can be used to supplement this performance. However, since higher oxygen-methane ratios also tend to consume more of the methane itself, this cannot be increased much and an optimum value exists with respect to the favorable production of pure hydrogen from the reactor permeate side.