Molybdenum (at 2.8, 3.3, 4.0 and 4.7 atoms nm(-2)) and cobalt (Co/(Co + Mo) ratios of 0.3, 0.4 and 0.5) were impregnated on wide-pore ZrO2-TiO2 mixed oxides (30-70) prepared with solvo-thermal treatment (80 degrees C, 1 day). Materials characterization comprised N-2 physisorption, XRD, thermal analyses, and UV-vis DRS, Raman, and IR spectroscopies. For impregnated dried materials (non-calcined) at concentrations beyond 3.3 atom nm(-2) and activated by sulfiding (H2S/H-2, 400 degrees C) no further improvement in activity in dibenzothiophene (DBT) hydrodesulfurization (HDS) (at 5.59 MPa, T = 320 degrees C) was observed. Thus, monolayer Mo dispersion was assumed at that content. The aforementioned formulation was chosen to be promoted by Co at different concentrations, the maximum HDS activity being found for sulfided catalyst with Co/(Co + Mo) = 0.4. Nevertheless, the promotion observed by Co addition was small (by a factor of similar to 3.2). The activity trends observed in the DBT HDS were well confirmed in the hydrotreatment of a real feedstock (straight-run gasoil). Dibenzothiophene reliably represented the behavior of organo-sulfur compounds present in the middle distillate, at the reaction conditions used in this study where sterically hindered compounds remained unreacted in the hydrotreated gasoil. (C) 2008 Elsevier B.V. All rights reserved.