USY faujasites (SiO2/Al2O3 = 12, 30 and 80) were used as hydrodesulphurization (HDS) catalyst supports. Mo, Co and P were impregnated at two concentrations: similar to 12.5, similar to 3 and similar to 1.6 mass %; similar to 18, similar to 5.5 and similar to 2.2 mass % (CL and HL series, respectively). Surface acidity decreased after Co-Mo-P deposition. Sulphided catalysts were tested in dibenzothiophene (DBT) HDS (320 degrees C, 5.59 MPa). The HDS rate slightly increased with both SiO2 content and Co-Mo-P loading. High selectivity to hydrogenated products suggested deficient Mo promotion in CL solids. Improved Mo promotion by Co (HL series) could be responsible for higher activity and marked selectivity to desulphurization to biphenyl.