The study of the water gas shift reaction performance in terms of complete conversions is presented. The behaviour of a membrane reactor (MR) consisting of a tubular microporous ceramic within a thin palladium membrane was compared with a membrane reactor using a palladium/silver membrane. Membranes were developed in order to obtain a metallic layer thick enough to avoid any defects of the metallic layer and ensure infinite hydrogen selectivity with respect to other gases. The lumen of both membrane reactors was filled with the catalyst. The experiments were carried out by using nitrogen as inert gas in the streep having a flow rate ranging between 1 x 10(-4) and 4 x 10(-4) mol s(-1) in co-current and counter-current mode in the temperature range 331-350 degreesC and in the feed molar flow range 3.05 x 10(-5) -7.1 x 10(-5) mol s(-1). Hydrogen was the only one gas passing through both membranes. A complete separation of hydrogen from the other gases of the reaction system was obtained. The water gas shift reaction conversion was close to 100% by using the Pd/Ag membrane. A mathematical model was developed to interpret the experimental data. It described the system under isothermal conditions and considered an axial differential mass balance in terms of partial pressure for each chemical species. The simulation study and the experimental results show a satisfactory agreement and both highlight the possibility to shift towards 100% the conversion of the considered reaction.