Drastic regulations concerning sulfur content in fuels has lead to and still imply numerous researches on hydrotreating reactions and hydrodesulfurization catalysts. The objective of this paper was to illustrate how, besides physicochemical characterization techniques, the kinetics could be also a useful and precious tool for the understanding of the reactions involved and of the catalysts used in this process. That was illustrated by application of competitive kinetics to the comprehension of the transformation of sulfur refractory compounds, of the H 2 S partial pressure effect on the activity of transition metal sulfides, and to the understanding of support effect for rhenium sulfide based catalysts.