A desulfurization system is operated in a manner which optimizes sulfur removal and octane retention. When the desulfurization reactor is operated at a specific ratio of total pressure to hydrogen partial pressure (P.sub.T/P.sub.H) and/or within a specific temperature range, optimum sulfur removal and octane retention are realized. The desulfurization reactor can be maintained at these optimized operating conditions by automatically adjusting one or more operating parameters of the desulfurization reactor in order to maintain a substantially constant hydrogen partial pressure (P.sub.H) in the reactor. Maintaining a relatively constant hydrogen partial pressure (P.sub.H) in the desulfurization reactor helps ensure a relatively consistent degree of desulfurization.