Extensive new measurements on pressure drop for the flow of purely viscous non-Newtonian fluids through packed beds made up of binary-and-quaternary size spheres are reported herein. These results have been interpreted using the previously available Sabiri and Comiti capillary model (1995), which has been quite successful in correlating the pressure drop data for the beds of uniform size spherical and nonspherical particles. The resulting predictions are also very good for mixed beds if some results are available for a Newtonian fluid, thereby enabling the evaluation of the tortuosity factor. However, since such data is always not available, an empirical scheme for estimating the tortuosity that allows the prediction of pressure drop with a mean relative error of about 10% is also presented. This sort of accuracy is quite acceptable for process engineering design calculations.