External wetting efficiencies were determined in a trickle-bed reactor by employing conversion data from the hydrogenation of the anthracene contained in an anthracene oil. Reactions were carried out at 573 K and 9.8 MPa on a sulfided Ni-Mo/gamma-Al2O3 catalyst. The results were compared with the total wetted area determined from the correlations based on the tracer method and developed by other authors. The discrepancy between both sets of data was attributed to the existence of a certain surface wetted by stagnant fluid whose fraction, f(s), was estimated from the comparison between tracer and reaction data. The correlations of Ring and Missen (1991) and Al-Dahhan and Dudukovic (1995), developed for high pressure trickle-beds, were employed to estimate f(s). A geometrical model has been employed to relate the static holdup with the fraction of surface covered by stagnant liquid which yielded an estimation of the mean distance between particles. The product of effectiveness factor and intrinsic rate constant were obtained for liquid- and gas-covered surfaces. Individual and overall effectiveness factors were estimated from a liquid phase intrinsic kinetic constant obtained in a previous work, showing that reaction took place preferably on the wetted surface.