Unpromoted and Pt, Pd, Ni and Ru-promoted molybdenum catalysts supported on amorphous silica-alumina (ASA) were characterized in the hydrodesulfurization of dibenzothiophene, and their activities were compared with a commercial Pt/ASA catalyst. The catalytic activity was found to increase in the following order : commercial Pt/ASA much greater than PtMo approximate to NiMo approximate to RuMo > PdMo approximate to Mo approximate to ASA. Characterization of the catalysts by XPS, TPR, and FTIR spectroscopy of adsorbed NO and pyridine confirmed that incorporation of 16.1 wt.-% Mo, minimized to a large extent the metal-support interaction, and decreased the acidity of the catalysts; although for the Ni-catalyst, the formation of Ni aluminate (and silicate) was not prevented. The incorporation of promoters enhanced molybdenum surface exposure and decreased the reduction temperature of MoO3; and for the Ni-promoted catalyst, increased the amount of sulfidable Ni species. Pd was not very effective as a promoter due to its poor dispersion, and the presence of a low percentage of active sites in the PdMo catalyst. For binary samples, a correlation was found to exist between the dispersion of MoS2 phases, the number of active sites titrated by NO, and the HDS activity of the sulfided samples.