This study compares the performance of laboratory trickle-bed and upflow reactors over a range of operating conditions, using the hydrogenation of a-methylstyrene to cumene in hexane solvent over 2.5% Pd on alumina extrudate catalyst as a test reaction. It is shown that the trickle bed performs better than the upflow reactor at low pressures when the reaction is gas limited, due to ready access of the gas to the incompletely externally wetted catalyst, while the upflow reactor performs better at high pressures when the liquid reactant limitation controls the rate, due to the completely wetted catalyst. Comparison of the two reactors at different pressures, liquid reactant feed concentrations, and gas flow rates is presented, and differences in performance are explained based on the observed shift from gas limitation to liquid limitation. Experiments in beds diluted with fines yield identical performances in both upflow and downflow modes of operation under both gas- and liquid-limited conditions, corroborating the fact that hydrodynamics and kinetics can be decoupled by using fines. It is also shown that the advantage of upflow or downflow depends on whether liquid or gas reactant is rate limiting and that a single criterion for identifying the limiting reactant can explain most of the data reported in the literature on these two modes of operation.