A new method using a batch gas-sweeping pervaporation was proposed for the measurement of different transport parameters of a polymer film to a solvent mixture. In addition to the total permeation flux and the selectivity of the film to the mixture, the diffusion coefficients and the permeation coefficients of the components can be determined. The method, which is based on new solutions of the second Fick law in which the upstream concentration is time-dependent, was applied to the transport of methanol-propan-1-ol mixtures through a cellulose triacetate membrane and their results were compared with those obtained in vacuum pervaporation. Both the methods give equivalent selectivity and permeation fluxes at all methanol contents. The diffusion coefficient of methanol, which was ca. 10(-7) cm(2)/s in cellulose triacetate when pure methanol was used, was found to be much smaller when methanol was mixed with propan-1-ol (ca. 10(-9) cm(2)/s). From the practical viewpoint, the cellulose triacetate membrane shows a high permeation flux with a rather good selectivity to methanol.