A process where the need to circulate hydrogen through the catalyst is eliminated is provided. This is accomplished by mixing and/or flashing the hydrogen and the oil to be treated in the presence of a solvent or diluent in which the hydrogen solubility is “high” relative to the feed. The type and amount of diluent added, as well as the reactor conditions, can be set so that all of the hydrogen required in the hydroprocessing reactions may be available in solution. The oil/diluent/hydrogen solution can then be fed to a plug flow reactor packed with catalyst where the oil and hydrogen react. No additional hydrogen is required, therefore, hydrogen recirculation is avoided and trickle bed operation of the reactors is avoided. Therefore, the large trickle bed reactors can be replaced by much smaller tubular reactor.