Pervaporation of water, ethanol and isopropanol through polydimethylsiloxane hollow fiber membranes was studied, with emphasis on elucidating the significance of permeate pressure build-up inside the fibers when the shell-feed mode of operation was used. The differential form of the Hagen-Poiseuille equation was used to describe the permeate pressure profile, and the theoretical predictions of permeate productivity were confirmed by experimental data. A parametric analysis showed that the dimensions of the hollow fiber (inside and outside diameters, and length) significantly affected the overall pervaporation performance of a hollow fiber membrane module, and the fiber dimensions must be optimized in order to achieve high productivity.