An appraisal has been made of the high-temperature properties of components of API group III, IV, and VI base oils by the method of catalytic oxidative thermolysis of fresh specimens and analysis of oxidation products. The low-temperature properties of oil components have been studied on a CCS-type cold-cranking simulator. Based upon the derived data, a basic matrix of ACEA class-C motor oils has been chosen for modern gasoline engines. Physicochemical transformations of individual base components and their blends thickened by a viscous polymeric additive under catalytic oxidative thermolysis conditions have been studied.