in a process for upgrading heavy asphaltenic oil , a feed slurry of a heavy asphaltenic oil and less than 10 ppm of molybdenum , e . g . molybdenum naphthenate , is contacted with a hydrogen - rich gas in a hydroconversion zone at hydrocracking conditions to convert at least a portion of said heavy oil to lower boiling products . this is achieved with minimum coke formation under moderate processing conditions .