A new residuum full hydroconversion slurry reactor system has been developed that allows the catalyst, unconverted oil, products and hydrogen to circulate in a continuous mixture throughout an entire reactor with no confinement of the mixture. The mixture is partially separated in between the reactors to remove only the products and hydrogen while permitting the unconverted oil and the slurry catalyst to continue on into the next sequential reactor. In the next reactor, a portion of the unconverted oil is converted to lower boiling point hydrocarbons, once again creating a mixture of unconverted oil, products, hydrogen and slurry catalyst. Further hydroprocessing may occur in additional reactors, fully converting the oil. The oil may alternately be partially converted, leaving a highly concentrated catalyst in unconverted oil which can be recycled directly to the first reactor. The slurry reactor system is, in this invention, preceded by an in-line pretreating step, such as hydrotreating or deasphalting. Following the slurry reactor system, fully converted oil may be subsequently hydrofinished for the removal of hetoroatoms such as sulfur and nitrogen.