The effect of oxygen compounds (guaiacol and phenol) on the hydrodesulfurization (HDS) of 4,6-dimethyldibenzothiophene (46DMDBT) and dibenzothiophene (DBT) was studied on a sulfided CoMoP/Al2O3 catalyst in a fixed bed microreactor (340 degrees C, 4.0 MPa). The reaction scheme of the transformation of guiaicol and of phenol (the main intermediate in the transformation of phenol) was established under deep HDS operating conditions. The transformation of phenol involved two main routes: a hydrogenation pathway (HYD) involving first the hydrogenation of the aromatic rings followed by C-O bond rupture (leading to the formation of benzene) and a direct deoxygenation (DDO) pathway involving only a C-O bond rupture (leading to cyclohexane). These two ways were independent, no transformation of benzene into cyclohexane was observed. Both oxygen compounds inhibited the hydrodesulfurization of sulfur compounds due to competitive adsorption between the oxygen and sulfur containing compounds, with the effect of guaiacol being stronger than the effect of phenol. The inhibition was similar in the transformation of 46DMDBT and DBT for the same oxygen molecule, showing that the two main routes (HYD and DDS) involved in the HDS were affected in the same way. This corresponds to a competitive adsorption between the oxygen and sulfur compounds containing on the catalyst surface according to a Langmuir-Hinshelwood model. (C) 2010 Elsevier B.V. All rights reserved.