The two approximate uptake rate expressions of spherical adsorbent pellets developed previously (Yao, C. and Tien, C. Approximation of uptake rate of spherical adsorbent pellets and their application to batch adsorption calculations. Chem. Eng. Sci. 1993, 48, 187) were applied to continuous-flow stirred tank and fixed-bed adsorption processes. The results show that both approximations represent improvement over the conventional linear driving force model. Relative accuracy of these two approximations was found to vary from case to case and can be related to the type of driving force for interphase mass transfer present in the particular problem.