Liquid and gas distribution in trickle-bed reactors was investigated in a column packed with commercial catalyst particles. Distilled water and air were used as liquid and gas phases, respectively. Surface tension effects were tested by adding detergent to the water. The influence of both liquid load and gas load on the distribution was studied. Flow rates corresponded to those used in industrial hydroprocessing units. It was found that the liquid distribution at a given liquid load can be improved considerably by either increasing the liquid load or flooding the column in advance. The gas distribution is shown to be correlated inversely with the liquid distribution. Use of a large-particle top layer results in an improved distribution.