to affect the age distribution a two stage system was utilized to give improved hydrogenation activity over a single stage unit but it not believed to be necessary to affect the observed change in product yields no interstage separation of gas and liquid was utilized during this study the feed stock used during this study was obtained from a mixture of vacuum residuum obtained from both domestic and foreign sources properties of the feed are shown in table i it should be noted that the feed is a nominal 1000 u00b0 f boiling point vacuum residuum examples 1 and 2 show the affects of varied reactor outlet hydrogen partial pressure accomplished by changing total reactor pressure at two different levels of 1000 u00b0 f conversion to 1000 u00b0 f material the reactor pressure was changed by changing the amount of back pressure held on the hydrocracking zone note the increase in all light hydrocarbon yields as the outlet hydrogen partial pressure increased this is unexpected and novel in light of examples 3 and 4 a nominal 1000 u00b0 f boiling point vacuum residuum was chosen for this experiment to obtain a feed typical of commercial operations it is suspected that lighter feeds such as atmospheric residuum or atmospheric gas oils would not give the same unexpected results seen in examples 1 and 2 the quantity of 650 u00b0 f minus boiling point material in these other feeds could be sufficient to inhibit the observed change in 650 u00b0 f minus yield table i______________________________________feed detailed data section total 1000 u00b0 f ______________________________________gravity api.