The objective of this study is a comparative analysis of single and two-membrane reactor performances for isothermal reversible gas phase reaction. The effects of flow patterns (ideal mixing, cocurrent and countercurrent plug flow) and the presence of inert components were investigated. It is shown by simulation that for the pure reactant feed in absence of inerts, the performance of a two-membrane reactor is not significantly affected by the flow patterns, providing the pressure ratio is kept close to zero. Concerning the conversion efficiency in the case when the reactant is the slowest permeating component, the advantage of a two-membrane reactor is evident, it being least significant for countercurrent plug flow. In the presence of inerts in the separation zone, the advantage of a two-membrane reactor is maintained, while it is diminished by increasing inert flow rate in the reaction zone.