A procedure has been developed for estimating the wetting efficiency in a trickle-bed reactor by using the conversion data obtained for a reaction following nonlinear kinetics. For this purpose, the hydrogenation of (x-methy I styrene on 0.5 wt% Pd/Al2O3 catalyst was studied in a batch slurry reactor (1.0-6.0 atm, 313-343 K), as well as in a trickle-bed reactor (313 K, 1.0-2.5 atm). The superficial velocities of gas and liquid in the trickle-bed reactor (TBR) were in the range of 0.25-1.0 cm/s and 0.06-0.24 cm/s, respectively. The intrinsic power-law kinetics, determined from the data obtained in the batch reactor, was used to calculate the effectiveness factors in the TBR. A comparison of these effectiveness factors with those calculated assuming complete external wetting showed that the wetting was not complete. The external wetting efficiencies (f) were determined using the method proposed by Ramachandran and Smith [AlChE J. 1979, 25 (), 538.]. To this end, effectiveness factors for the catalyst completely covered with gas or liquid were estimated for this nonlinear kinetics by a previously published procedure. f varied between 40% and 75% with the liquid superficial velocity. The difference between f values calculated from the conversion data and from the correlation developed using residence time distribution (RTD) data was attributed to the presence of stagnant liquid zones between the catalyst particles.