Oxidative desulfurization reaction (ODS) of Straight Run Gas Oil (SRGO) was carried out on a CoMoP catalyst, classically used in hydrotreatment. Optimum Co/Mo ratio for the ODS reaction was found at 0.5, which also corresponds to an optimum ratio for HDS. This catalyst allowed to oxidize sulfur compounds to more polar sulfones which can be adsorbed on the catalyst and served as modifying agent. The catalyst before and after ODS and the CoMoP catalyst modified by a commercial dibenzothiophene sulfone (DBTO2) were tested in gas oil HDS and better performances were obtained for the modified catalysts for a sulfone content of 10 wt%. This effect was attributed to the redispersion of cobalt species observed after modification, leading to more efficient promotion.