The water gas shift (WGS) reaction is an important step of hydrogen production in industrial cycles for upgrading H, rich streams by CO conversion present in syngas mixtures. WGS was studied in a Pd-alloy membrane reactor (MR) by means of a non-isothermal mathematical model using, as main parameter, Damkohler's number (Da), the ratio of characteristic times of flow rate and reaction, in a temperature range of 220-320 degrees C. Two different reactant equimolecular feed streams were considered: one containing only CO and H2O the other containing also H-2 and CO2 Of higher industrial interest. The permeation driving force was generated by feed pressure ranging 200-1500 kPa which allows a good H-2 recovery index (up to 95%) and a retentate stream rich (up to 80%) in CO2. No sweep gas was used; therefore, a pure H-2 stream is obtained as permeate. CO conversion, H-2 recovery index and its partial pressure are the main variables used for analysing the MR performance and showing its advantages with respect to a TR in the large feed pressure range. In addition, the volume index and conversion index are introduced for the first time and proposed as simple tools analysing the volume reduction or improved conversion shown by MRs; both lead to the catalyst amount and reactor size being reduced. The two new indexes proposed by membrane engineering open a window on the analysis of MRs for H-2 production and CO2 separation for the process intensification strategy. This paper describes a modelling analysis of a packed-bed membrane reactor involving dense Pd-Ag commercial permselective membrane. (c) 2007 Elsevier B.V. All rights reserved.