A study of the performance of a membrane reactor (MR) for the water gas shift (WGS) reaction is presented, also pursuing the membrane engineering approach in the logic of the Process Intensification Strategy. The MR mathematical model was developed from the design equation of traditional reactors considering a H-2 high-selectivity membrane, to perform a comparison between the two reactor types and experimental literature data(8) and qualitatively and quantitatively estimate the convenience of MR use. The effect of the operating conditions (temperature, reaction pressure, feed flow rate, etc.) on the catalyst efficiency was also considered in addition to their influence on the reaction from kinetic and thermodynamic points of view. A catalyst effectiveness factor was calculated considering the Thiele module. It takes into account the kinetic and diffusive resistances inside the catalytic pellet, which also depend on the pellet geometric characteristics (pore diameter, pore length, tortuosity, porosity, etc.). The obtained results confirmed the advantage of the use of a MR for the WGS reaction, in terms of conversion improvement and reduction of the necessary reaction volumes and related costs.