The rate of hydrogenation of cottonseed oil has been studied experimentally in an agitated slurry reactor. The data have been compared and discussed with most of the literature data on the subject, in light of a model for this reaction. The model was based on a dual-site surface reaction mechanism on the catalyst particles, taking into consideration mass transfer resistances affected by agitation. It was shown that chemisorption of hydrogen is significant only at pressures higher than about 10 atm. At lower pressures, the reaction was pseudo-second order, at a given catalyst concentration. It has been possible to separate chemical rate constants from the masstransfer effect and correlate them with temperature.