Hydrodynamics, uniform wetting of the catalyst surface and transport of reaction components show a strong influence on the overall performance of a trickle-bed reactor. The aim of the paper was finding limits for predominant effects of the catalyst wetting, oxygen transport and surface reaction in a catalytic wet oxidation of aqueous solutions of phenol, which is a typical bactericidal pollutant, undesirable in the environment. A threephase high-pressure laboratory tubular reactor 18 mm in diameter with catalyst bed length 200 mm was run at 130-170 ^oC, pressures 2-7 MPa and space velocity 1-20 h^-1. Oxidation activities of two catalyst types, CuO on a silicate carrier (Cherox® 46-00) and extruded active carbon (Chemviron®) were compared. At a comparable loading, active carbon showed a higher catalytic activity. For elimination of the effect of nonuniform distribution of liquid and achieving a perfect wetting of the catalyst surface with liquid, the catalyst beds diluted with 1-mm glass spheres were also tested. However, under conditions, when the resulting oxidation rate is limited by the transport of a key component from the gas phase (oxygen), the uniform wetting of the catalyst surface with the reaction mixture leads to a lower performance of the oxidation reactor due to a lower interphase area caused by a higher liquid hold-up.