Degradation reactions of ethylene-propylene copolymers at a high temperature (380-430A degrees C) and a high pressure (180-220 atm) in the presence of a nickel catalyst and hydrogen have been studied. In contrast to the previously known processes, the degradation reactions have been conducted simultaneously with hydrogenation reactions. The effects of temperature, pressure, and time on the yield of each fraction have been examined. As a result, optimal process conditions have been found for each fraction. The physicochemical properties of the lube oil fraction (C-18-C-25) used as a base oil have been studied. It has been found that as in the case of oils derived from ethylene-propylene copolymers by other methods, these oils have a high viscosity index (VI > 95), a high flash point (T (f) > 210A degrees C), and a low pour point (T (p) < -50A degrees C).