The catalytic hydrodenitrogenation of heavy petroleum fractions is important for the production of high-quality fuels, because the nitrogen-bearing compounds poison acidic catalysts and inhibit sulfur removal. Two families of synthetic nitrogen-containing model compounds representative of asphaltene molecular structures were catalytically hydrogenated over a commercial NiMo/gamma Al2O3 catalyst under industrial hydrotreating conditions, i.e., 370 degrees C and 18 MPa of hydrogen for 1 h, in a stainless steel batch reactor. The bridged compounds with pyridine as a center ring gave cracking, hydrogenation, and hydrodenitrogenation products with selectivities that depended on the position of substituents on the central pyridine ring. In contrast, a series of fused cholestane-benzoquinoline compounds gave only hydrogenation of all-carbon aromatic rings.