The knowledge of sorption of vapors and liquids in polymer membranes is important for the derivation of structure-property relationships between the polymer structure and membrane performance, which facilitates preparation of better membranes. Experimental methods for the determination of sorption are tedious and expensive. Conventional predictive methods are often inadequate. In this work, a combination of the Cosmo-SAC model based on quantum chemical calculations and the Flory-Rehner equation is used to predict the sorption in polymer membranes. A single adjustable parameter is used for each polymer. It is shown that the model can adequately predict sorption in several membrane polymers including block copolymers for both single component and two component sorption. In addition, two component sorption data can be predicted from single component sorption data. Further, the measurement of the sorption of a pure liquid in a polymer by simple swelling experiments is sufficient for obtaining initial estimates of single component sorption over the entire activity range as well as the two component sorption from liquid mixtures over the entire activity range. Hence, the use of complex equipment and tedious multicomponent sorption experiments can be minimized or avoided. This significantly simplifies the experiments required for measurement of sorption in polymer membranes. (C) 2012 Elsevier B.V. All rights reserved.