An experimental parametric Study on wetting efficiency is reported which evaluates the influence of liquid viscosity, as well as the effect of particle size(/shape) and bed porosity (epsilon(B)), separately. A 10-fold increase of liquid viscosity improves slightly catalyst wetting (by about 10%), while an increase of either bed porosity or particle size has the opposite effect. Wetting efficiency is reduced by about 0.1 for an increase Of epsilon(B) from 0.38 and 0.40 due to a change of particle size from 1.8 to 7 x 10(-3) in while the decrease is only 0.05 for a similar variation Of epsilon(B) (0.38-0.41) with the same particles. The effect of particle shape (cylindrical/trilobe extrudates or spheres) appears very small in the investigated conditions. A new correlation for wetting efficiency is proposed, using a bounded function and only three dimension less groups (liquid Froude and Morton numbers and bed porosity). This correlation is able to predict wetting efficiency with a very good precision on a large database, provided wetting liquids are used. Adding fines in the fixed bed is also examined, and its positive effect can be correlated with the size ratio between catalyst particles and fines.