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.