oils hydrocracking residual oils and thermal cracking residual oils as a property of the raw material it is preferred that the sulfur content vanadium content nickel content and asphaltene content in the raw material become as small value as possible these oils may be used alone or as a mixture of them the above described petroleum heavy residual oils are subjected to hydrogenation treatment in the presence of a hydrogenation catalyst under conditions comprising a temperature of 370 u00b0 to 450 u00b0 c preferably 380 u00b0 to 410 u00b0 c a pressure of 70 to 210 kg cm 2 g preferably 150 to 200 kg cm 2 g a liquid space velocity of 0 4 to 2 0 hr 1 preferably 0 4 to 1 0 hr 1 and a ratio of hydrogen oil of 700 to 1 700 nm 3 kl preferably 700 to 1 500 nm 3 kl by carrying out the hydrogenation treatment impurities present in the heavy residual oils such as sulfur nitrogen and metals etc are removed and at the same time the amount of high molecular polycyclic aromatic components such as asphaltene is reduced the conditions of the hydrogenation treatment are fixed so as to result in a sulfur content of the hydrogenated residual oil of 0 7 by weight or less a vanadium content of 10 0 ppm or less a nickel content of 5 0 ppm or less and an asphaltene component of.