A membrane reactor with separated feed of reactants is demonstrated as a promising contractor type when dealing with heterogenously catalysed, very fast and exothermic gas phase reactions. Due to the separation of reactants a good control of the system is obtained, because process variables can be varied independently from each other. Transport of reactants is the rate governing process and because this is only slightly temperature dependent a thermal runaway will not occur. When dealing with e.g. combustion process no explosive mixtures will build up and safety is increased. Based on the dusty-gas model, the concentration profiles of components inside the membrane can be calculated together with the fluxes. However this is a calculation time consuming process and not necessary in all cases. In absence of a pressure drop and no slip of reactants to the opposite side a linearisation is possible leading to a simplified expression for the interfacial flux of a reactant and a criterion to evaluate the possibility of slip of reactants. Using the oxidation of carbon monoxide catalysed by platinum as a model reaction this approximation was experimentally verified by comparison of measured fluxes with the calculated results. Apart from flux measurements exploratory overall conversion measurements were carried out with the membrane reactor module in order to demonstrate its operation performance. From these studies it was concluded that conversion levels up to 90% carbon monoxide could easily be achieved.