Hydrogenation of a-methyl styrene (AMS) to cumene at 40 degreesC in a downflow trickle bed was used as a test reaction for an investigation of the prediction of the performance of trickle-bed reactors. Dynamic and static saturation are well predicted by several models but pressure drop cannot be accurately estimated by correlations now in the literature. This raises doubts about the use of mass transfer models which employ pressure drop taken from the literature. The simple film model for predicting conversion fails in the high-interaction regime at least with foaming liquids. A correction to the model to allow for the effect of foam on mass transfer characteristics is proposed but was not independently tested.