It has previously been demonstrated that pennselective membranes can increase the yields of hydrogen, improve the product quality and minimize or even eliminate the adverse effect of system pressure in catalytic steam methane reforming. At the same time, oxygen addition can lead to autothermal operation by providing some or all of the required endothermic heat of the reforming reaction. Previous comparison of reactor model predictions with experimental results has demonstrated, at least for the fluidized bed membrane reactors (FBMRs) investigated so far, that the product distribution in the non-permeate stream approaches very closely to the shifted chemical equilibrium after allowance is made for the removal of hydrogen. In this paper, we adapt an equilibrium model devised for gasification to predict the influence of various process parameters. It is shown that it should be possible to operate autothermally and free of coke formation over a considerable range of temperature, pressure and steam-to-methane ratio. (C) 2001 Elsevier Science B.V. All rights reserved.