Methods are provided for selecting optimal operating conditions for the hydrodesulfurization of a liquid hydrocarbon feed in a reactor. According to one aspect, a desired sulfur content of the product stream is selected. The carbazoles content of a first liquid hydrocarbon feed is measured, and a reaction order for the first liquid hydrocarbon feed is calculated based on the measured carbazoles content. An operating severity index based on the calculated reaction order is then calculated. According to one aspect, the operating severity index comprises an operating temperature of the reactor to yield the product stream with the desired sulfur content from the first liquid hydrocarbon feed. According to another aspect, the carbazoles content of a plurality of liquid hydrocarbon feeds are measured to generate a database of the measured carbazoles content.