The interaction between the isomeric xylenes and different cellulose esters was investigated using solubility parameter considerations and through measurements of swelling values. p]Hansen's three-dimensional solubility parameters δd, δp, δh of all the components have been calculated. These values have been used to predict the interaction between polymer and penetrant. A measure for this interaction is given by Δ, which is the distance between polymer and penetrant in the δd, δr, δh space. As expected, the experimental swelling values varied in inverse proportion to the calculated Δ values. p]Pervaporation characteristics of different cellulose ester membranes were determined by measuring product rates and selectivity. The differences in membrane characteristics have been explained qualitatively in terms of the solubility parameter concept.