Models are developed for simulation of membrane reactors for the high temperature shift conversion of carbon monoxide (GO). Three configurations are considered in the analysis; the first employs a shell and tube arrangement, where the catalyst is placed inside the tubes which have hydrogen-permeable walls. The second and third configurations make use of an existing HTSC system plus membrane separation cells for removal of hydrogen from the feed (second configuration) and from the feed and effluent reaction mixture leaving the first catalyst bed in the reactor (third configuration). For the first configuration, in situ reaction and separation of hydrogen takes place. Accordingly, a shift from equilibrium occurs along the reactor length as a result of continuous removal of hydrogen present in the feed and formed during reaction. On the other hand, a shift from equilibrium in the second and third configurations relies on the use of separate membrane cells for hydrogen removal. CO conversions up to 0.99 are predicted in the first and third configurations which implies that the CO content in the effluent is below the maximum limit of 0.25 mole percent on a dry basis. Currently, this limit is achieved by use of both high and low temperature shift converters. This result suggests the possibility of the reconfiguration of a conventional CO shift conversion system, where it is feasible, to eliminate the low temperature converter. Although both the first and third configurations meet the desired limit on CO content in the effluent, it is found that the amount of catalyst needed for the first configuration is much larger (more than five times) than that of the third configuration.