In the upgrading of heavy petroleum oils and residues by hydrotreating, multiple-reactor fixedbed units loaded with different types of catalysts are extensively used. Catalysts for such hydrotreating processes are chosen on the basis of activity, selectivity, and life. The performance of the overall hydrotreating process with regard to various reactions, such as hydrodemetallation (HDM), hydrodesulfurization (HDS), hydrodenitrogenation (HDN), asphaltenes cracking (HD-Asph), and conversion to distillate and catalyst life-on-stream, is clearly linked to the performance of the catalyst in different reactors. Information regarding the activity, selectivity, kinetics parameters, and deactivation of the individual catalysts are, therefore, highly desirable for optimizing reactor loading in a multiple catalyst system. In the present work, a comparative study was conducted on the kinetics of various reactions such as HDS, HDV, HDNi, HDN, CCR reduction, and asphaltenes conversion in hydrotreating Kuwaiti atmospheric residue (KU-AR) over three types of catalysts. The results showed diverse kinetics behavior of different hydrotreating reactions. The diverse kinetics behavior of the different reactions and the strong dependence of the kinetics parameters on catalyst type are consistent with the kinetic aggregation theory. The results are discussed in comparison with those available in published literature.