Abstract: Heavy oils containing metal contaminants are hydrodesulfurized in a reactor containing a series of fixed beds of catalyst. The catalyst particles become caked together during the hydrodesulfurization process, possibly due to formation of metal sulfides and carbonaceous deposits, and the caked catalyst is removed by a hydro drilling method. The hydro drilling is preferably commenced by drilling a central opening through the catalyst beds. The catalyst particles and chunks are cut from the bed and removed from the reactor vessel through catalyst dump openings at the bottom of the vessel. Preferably, the dump openings are maintained open by hydro lancing as the cutting of catalysts in the upper part of the vessel loosens the catalyst so that the catalyst will drop down the central opening and thus out through the catalyst dump openings at the bottom of the reactor vessel.