The degree of hydrogenation of various classes of aromatic and olefin hydrocarbons in the cat cracking light gas oil hydrofining process in the presence of Al-Co-Mo and Al-Ni-W catalysts is studied. The Al-Ni-W catalyst exhibits much greater hydrogenation activity with respect to aromatic hydrocarbons than the Al-Co-Mo catalyst. However, the Al-Co-Mo catalyst exhibits much greater hydrogenation activity with respect to olefin hydrocarbons than the Al-Ni-W catalyst.