Trickle-bed reactors are frequently used in bench scale and pilot plant experiments to determine reaction kinetics and generate data for commercial scale-up. Depending on experimental conditions, these reactors sometimes cannot produce accurate data if the influences of three main factors (plug flow deviation, external wetting efficiency, and reactor wall effect) on reactor performance are not property minimized or eliminated. Therefore, it is highly desirable to operate a trickle-bed reactor at conditions at which these effects can be neglected so that reliable and repeatable data can be obtained. There have been various criteria reported in the literature to theoretically determine the influence of these factors. The objectives of this work are to conduct an extensive review on the studies related to these criteria and to further make recommendations as how to use these criteria to provide guidelines for designing experiments. (C) 2008 Elsevier B.V. All rights reserved.