A method for preparing a sulfided molybdenum catalyst concentrate which method comprises: (a) forming a precursor catalyst concentrate by mixing together: (i) a hydrocarbonaceous oil comprising constituents boiling above about 1050.degree. F.; (ii) a metal compound, said metal being selected from the group consisting of Groups II, III, IV, V, VIB, VIIB, and VIII of the Periodic Table of the Elements, in an amount to provide from about 0.2 to 2 wt. % metal, based on said hydrocarbonaceous oil; and (iii) elemental sulfur in an amount such that the atomic ratio of sulfur to metal is from about 1/1 to 8/1; and (b) heating the mixture to an effective temperature to produce a catalyst concentrate.