Low CO for increased naphtha desulfurization

Naphtha hydrodesulfurization selectivity is increased by reducing the amount of CO X (CO plus ½ CO 2 ) in the hydrodesulfurization reaction zone to less than 100 vppm. While this is useful for non-selective hydrodesulfurization, it is particularly useful for selectively desulfurizing an olefin-containing naphtha without octane loss due to olefin saturation by hydrogenation. The CO X reduction is achieved by removing CO X from the treat gas before it is passed into the reaction zone.