Processes for the treating of sulfur-containing petroleum oil feedstocks employing alkali metal compounds, alkaline earth metal compounds, and mixtures thereof are disclosed. Specifically, processes for hydrotreating feedstocks which have been previously partially desulfurized using conventional hydrodesulfurization catalysts by contacting such feedstocks with alkali metal compounds, alkaline earth metal compounds, and mixtures thereof, are disclosed. Preferably, the products of such a treatment are employed as feeds for catalytic cracking processes. In addition, processes for the combined hydrotreating and hydroconversion of various sulfur-containing petroleum oil feeds are disclosed, employing at least two hydroconversion agents selected from the group consisting of the alkali metal compounds and alkaline earth metal compounds, in the presence of added hydrogen, and at elevated temperatures. The reaction products formed thereby include a substantially desulfurized and demetallized, as well as a significantly upgraded petroleum product. The latter is demonstrated by a reduced Conradson carbon content and an increased API gravity.