Abstract: An improved hydrogen donor diluent cracking process for upgrading hydrogen deficient hydrocarbonaceous materials such as petroleum residua to more valuable liquid distillates. The hydrogen donor diluent, which is a material that has been partially hydrogenated and which readily gives up hydrogen under thermal cracking conditions, is injected into the cracking unit at a plurality of points so that the ratio of the rate of hydrogen transfer to the rate of cracking is more uniform throughout the cracking unit than if all the hydrogen donor diluent is injected with the feed charge to the cracking unit.