The relationship between molecular structure and hydrogenation reactivity in heavy oil hydroprocessing was sought via the elucidation of the controlling reaction pathways and kinetics of one-, two-, three-, and four-fused ring compounds. Hydrogenation reactions of o-xylene, tetralin, naphthalene, phenanthrene, anthracene, pyrene, and chrysene and their multicomponent mixtures were studied in cyclohexane solvent using a presulfided CoMo/Al2O3 catalyst in an 1-L batch autoclave at P-H2 = 68.1 atm and T = 350 degrees C. Quantitative network analysis allowed estimation of 45 hydrogenation rate; parameters and an equal number of equilibrium ratios for 36 aromatic and hydroaromatic compounds. These values were then used in the evaluation of five adsorption parameters for aromatic ring number-based lumps from the multicomponent mixture experiments. Three classes of hydrogenation were discerned, based on the magnitude of numerator rate parameters. The adsorption parameters clearly increased with increasing aromatic ring number.