TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: In the process, where each partial stream of hydrogen containing gas following in downstream direction is larger than the preceding one by essentially the same factor as the corresponding partial streams of raw material feed with which they are mixed. The hydrogen excess is at least 50%, preferably 100-300%. The reactor system comprises more than 3, preferably more than 5, but less than 20, preferably less than 10 catalyst beds. The atomic ratio of the hydrogenation catalyst of the metal (or metals) from group VIII to the metal (or metals) from group VIB is 0.01-0.03. The hydrogenation catalyst contains a quantity of phosphorus which is strictly more than 1 wt.% and less than 8 wt.% of oxide phosphorus pentoxide with respect to the total catalyst mass. The hydrogenation catalyst is used only in the first catalyst bed and another hydrogenation catalyst comprising at least one element from group VIE and at least one element from group VIII, and at least one refractory oxide support of alumina and silica alumina, the element from group VIB comprises molybdenum and tungsten, the element from group VIII comprises nickel and cobalt, the elements being in the sulfide form, is used in the catalyst beds following the first one, and the hydrogenation catalyst displaying an atomic ratio of the metal (or metals) from group VIII to the metal (or metals) from group VIB is 0.1-1. The weight ratio of added diluting agent to raw material feed at the reactor entrance is 4:1 or less and each partial stream of fresh raw material feed as well as each partial stream of hydrogen containing gas is by a factor of 1.25 or more larger than the previous partial stream. The weight ratio of added diluting agent to total raw material feed is less than 1, preferably less than 0.5. The amount of the partial streams or the partial mixed streams to the second and, if present, the following catalyst beds is controlled so as to adjust the temperature at the inlet of every catalyst bed to essentially the same temperature as at the reactor inlet at the first catalyst bed. The active phase of the hydrogenation catalyst is constituted by one element comprising VIB, where the element from group VIB is molybdenum, and one element from group VIII, and the element from group VIII is nickel. The hydrogenation catalyst is used in every catalyst beds of the fixed bed reactor system, where the step of hydrogenation takes place at a hydrogen partial pressures of 1-8 MPa, and at a temperatures of 145-280 degrees C. The liquid hourly space velocity of the raw material feed in each bed is 0.1-5 m3/m3 catalyst/hour.