(57) The invention relates to a process for the upgrading of heavy, viscous hydrocarbonaceous oils, comprising fractionally distilling said hydrocarbonaceous oil to produce at least one distilled fraction and a residuum without substantially cracking said hydrocarbonaceous oil, contacting said residuum with a liquid hydrogen donor material stream to produce a hydrocracked stream and separating said hydrocracked stream into a gaseous stream and a liquid hydrocracked stream, characterized in that:

(a) said liquid hydrocracked stream is fractionally distilled to separate from higher and lower boiling fractions a hydrogen donor precursor stream boiling above a temperature from substantially 180°C to substantially 200°C and below a temperature from substantially 330°C to substantially 350°C,

(b) at least part of said hydrogenated hydrogen donor material is recycled as the material which constitutes the entire liquid hydrogen donor material stream to contact said residuum.