The kinetics of the liquid-phase hydrogenation of naphthalene and tetralin (1,2,3,4-tetrahydro-naphthalene) in decane was studied on a commercial nickel catalyst at 80-160 degreesC and 20-40 bar in a CSTR. The proposed kinetic model assumes three adsorption modes (pi-, pi/sigma-, and a-adsorption), of which two are associative and one is dissociative. The associatively adsorbed aromatic compounds are assumed to be active in hydrogenation, whereas the dissociative adsorption leads to coke formation, Moreover, it is proposed that naphthalene adsorption occurs on a single active site, whereas tetralin adsorption requires an ensemble of Ni atoms. This explains the nonlinear decrease in the tetralin hydrogenation rate with catalyst deactivation, whereas the naphthalene hydrogenation decreases linearly. The proposed reaction and deactivation mechanism is able to describe the main features of the observed kinetics, including the formation of octalins (octahydronaphthalene), changes in the cis-to-trans selectivity of decalin (decahydronaphthalene), and the difference between the naphthalene and tetralin hydrogenation and deactivation rates.