Processes for the simultaneous desulfurization and hydroconversion of heavy carbonaceous feeds, including various sulfur-containing heavy petroleum oils, are disclosed. These feeds are contacted with alkali metal hydroxides in a conversion zone, in the presence of added hydrogen, and at elevated temperatures, whereby the feeds are substantially desulfurized, while at the same time significant upgrading of these feedstocks is obtained as demonstrated by decreased Conradson carbon, increased API gravity, and the conversion of a substantial portion of the 1,050.degree. F+ portion of the feedstream. In addition, methods for the regeneration of alkali metal hydroxides from the alkali metal salts produced in the conversion zone are disclosed.