In the hydroconversion of carbonaceous materials such as hydrocarbonaceous oils and coal or mixtures thereof, in which inorganic poly acids comprising molybdenum or tungsten or salts thereof are used as catalyst precursors which are converted to catalysts, the use of a combination of phosphoric acid and said poly acids or salts thereof as catalyst precursor wherein the amount of phosphoric acid is such as to provide from about 0.5 to about 3.5 atoms of phosphorus per atom of molybdenum or tungsten results in a catalyst having improved activity.