A cell model was introduced and an analytical solution was obtained to describe the shell side mass transfer problem in a parallel flow hollow fiber membrane module. To develop the analytical model, a uniform fiber arrangement was assumed, and the shell side flow was described by Happel's free surface model, and the boundary condition of a uniform fiber wall concentration was taken into account. The analytical solution showed that the shell side Sherwood number (Sh) was the function of Graetz number (Gz) and the module packing density (Phi). Experiments involving the absorption of CO2 into water with polypropylene hollow fiber. membrane module were performed. It was found that the experimental results could be described by Sh = (0.163 + 0.27phi)Gz(0.6). The. experimental mass transfer coefficient was higher than that predicted by the model when the packin density of the module, was 20%, whereas it was lower than the predicted value when increasing the packing density exceeded 30%. This experimental correlation together with the analytical solution might provide a useful tool to model and scale up the corresponding membrane contactor process.