Rubbery polymeric membranes demonstrate potential in gas separation as they can be selective for carbon dioxide over less condensable gases such as hydrogen. In many industrial processes where these membranes are applicable, minor gas components such as carbon monoxide, hydrogen sulfide and water are present. Here, the effect of these minor components on the performance of a polydimethyl siloxane rubbery membrane in CO(2)/N(2) separation is experimentally determined. The permeability of CO(2) through PDMS is reduced upon exposure to CO, H(2)S and water, due to competitive sorption of these gases into the polymeric matrix. Similar behavior is observed for N(2); however the presence of H(2)S gives rise to an observed increase in N(2) permeability. Extension of the Flory-Huggins theory to a quaternary system allows the relevant interaction parameters for this system to be determined. Upon exposure to a wet feed, CO(2) and N(2) permeability decrease due to water occupying free volume within PDMS, with the Flory-Huggins interaction parameters indicating mixing of CO(2) or N(2) with water within PDMS is highly unfavorable. Quantitative analysis of the change in permeability of CO(2) and N(2) in PDMS in the presence of these minor components enables more accurate prediction of membrane performance in industrial applications to be undertaken. (c) 2010 Elsevier B.V. All rights reserved.