A compartment model was developed to describe the flow pattern of gas within the dense zone of a membrane-assisted fluidized-bed reactor (MAFBR), in the bubbling mode of operation for steam reforming of methane both with (adiabatic) and without (isothermal) entering oxygen. Considering such a flow pattern and using the experimental data reported elsewhere [Roy S, Pruden BB, Adris AM, Grace JR, Lim CJ. Fluidized-bed steam methane reforming with oxygen input. Chem Eng Sci 1999; 54:2095-2102.], the parameters of the developed model (i.e., number of compartments for the bubble and emulsion phases) were determined and fair agreements were obtained between model predictions and experimental data. The developed model was utilized to describe the behavior of an industrial scale adiabatic and isothermal MAFBR. Moreover, the influences of various operating and design parameters such as steam-to-methane ratio (SMR), oxygen-to-methane ratio (OMR), operating temperature and pressure, and the number of hydrogen membrane tubes on the performance capability of the MAFBR were investigated. Furthermore, the performance capability of the MAFBR was optimized subject to the various operating and design constraints, including 1 <= SMR <= 4 and 500 <= T <= 1250 K, in the bubbling regime. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.