An implicit one-dimensional two-zone two-fluid mechanistic model was developed for the prediction of the irrigated two-phase pressure drop, the total liquid holdup, and the packing fractional wetted area in gas-liquid countercurrent columns containing structured packings and operated in the preloading zone. The model was an offshoot of the well-known "single-slit" mechanistic approach to cocurrent down-flow trickle-bed reactors. It mimicked the actual bed void by means of two hypothetical, recurrent, and geometrically similar inclined slits consisting of a dry slit and a wet slit. This mechanistic model required no single adjustable parameter and proved powerful in the prediction of the column hydraulics under various operational conditions such as atmospheric scrubbing or high-pressure/temperature distillation conditions. In this context, a collection of data relative to the irrigated pressure drop, liquid holdup, and packing fractional wetted area, obtained under low/high pressure/temperature has been compiled from the literature for columns equipped with structured packings and operated below the loading point and under partial wetting. This databank provided pertinent information for successful validation of the model. The satisfactory results obtained highlight the breadth of applicability of the proposed approach, especially for new designs or for optimal rating of existing equipment.