A simple mass transfer model for the pervaporation process. the key component model, is described. in pervaporation the selectivity is often of the sorption type, which means that at the upstream side of the membrane, one of the components is much more sorbed than the others. The diffusivity of each component in this model does only depend on the volume fraction occupied by the key component. With this approximation when to solvents are involved in the pervaporation process the classical 6-parameter model becomes a four-parameter model. We develop the mass transfer equations in a special case where the diffusivity of each pure component follows Long's equation with a common plastization coefficient. The key component model is checked with data concerning pervaporation of ethanol-water mixtures through a PVA based membrane that follows these conditions. The limiting diffusivities and piastization coefficient are obtained from equilibrium and pervaporation data (at nil downstream pressure). The model allows the prediction of the pervaporation fluxes at growing downstream pressure. (c) 2009 Elsevier B.V. All rights reserved.