The hydroprocessing of mixtures simulating a coal liquid without organonitrogen compounds was investigated with a once-through flow reactor operated with liquid-phase reactants at 350-degrees-C and 171 atm. The catalyst was sulfided Ni-Mo/gamma-Al2O3. The reactants included pyrene, phenanthrene, fluoranthene, dibenzothiophene, dibenzofuran, and 5,6,7,8-tetrahydro-1-naphthol. The products formed from each reactant were determined, and each reaction was modeled as first order in the organic reactant. The reactivity of fused six-ring aromatics increases with the number of rings, but the change from one member of the family to another is less than the order-of-magnitude increase in reactivity from benzene to naphthalene. Fluoranthene must be considered in a separate compound class from fused six-membered-ring aromatics because it is hydrogenated more rapidly. Dibenzothiophene gives biphenyl selectively. Dibenzofuran reacts very slowly, whereas 5,6,7,8-tetrahydro-1-naphthol reacts very rapidly. The results reported here, in combination with the reaction networks developed in the sequel, are the first quantitative evaluation of reactivities of components in a mixture simulating a hydroprocessing feedstock that take account of competitive reactions and the formation of intermediate products.