A generalized slit model was developed for the prediction of frictional two-phase pressure drop, liquid holdup and wetting efficiency in trickle flow reactors operated under partially and fully wetted conditions. The present model was a generalization of Holub mechanistic model where partial wetting was incorporated to account for contributions from dry pellet-gas, liquid-wet pellet and gas-liquid interface shear stresses to the frictional pressure gradient. This proposed model mimicked the actual bed void by two geometrically identical inclined slits, a wet slit and a dry slit. High-pressure and high-temperature wetting efficiency,liquid holdup and pressure drop data reported in the literature for trickle flow regime using conventional monosized beds and binary catalyst pellets-fines mixed beds were successfully forecasted by the model. The model also proved powerful in demarcating the changeover between the partially wetted and the fully wetted pellet conditions.