The ellipsometric characterization of the CO2 sorption of a silica membrane provides a fast and accurate technique for the characterization of maximum sorption and the heat of adsorption. Both parameters are evaluated for the 73 nm thick silica layer as well as the 1650 nm thick supporting gamma-layer. The applicability of ellipsometry for studying sorption of supported membranes relies on a careful analysis of the membrane prior to sorption measurements. (C) 2004 Elsevier B.V. All rights reserved.