Experimental studies (Lutran et al., Ind. Engng Chem. Res. 30 (1991) 1270; Ravindra et al., Ind. Engng Chem. Res. 36 (1997) 5133) and numerical simulation (Jiang et al., Chem. Engng Sci. 54 (1999) 2409-2419) lead to the conclusion that fluid flow distribution in trickle beds is a function of bed structure (i.e. porosity distribution), particle external wetting and inlet superficial velocities of the two fluids. In this study, quantitative relationships among the above parameters are developed in a statistical manner through a series of computational fluid dynamics simulations. The contribution of capillary forces to liquid maldistribution is significant in the case of partial particle external wetting; however, it is shown that the effect of porosity non-uniformity in packed beds can be reduced if the particles are prewetted well.