This study addresses some of the inhibiting aspects of the hydrodesulfurization (HDS) of 4,6-diethyldibenzothiophene on a sulfided CoMo/Al2O3-SiO2 catalyst at relatively low hydrogen pressures. It is shown that thermodynamic equilibrium does not play a significant role in inhibiting sulfur removal at 2.17 MPa hydrogen pressure at least up to 370 degreesC. Both 3-ethylcarbazole and naphthalene inhibit the HDS rate, with the former being far more potent. Other electron-rich or electron-deficient substituted carbazoles are also strong inhibitors, suggesting that the substituent-induced electronic effect is not a factor governing the poisoning potency of the carbazole family. Operating at high temperatures is more effective in mitigating the inhibiting effect than operating at high hydrogen pressures. A strong inhibiting effect can lead to falsification of the overall HDS kinetics. (C) 2003 Elsevier Inc. All rights reserved.