A method for selecting optimal operating conditions for the hydrodesulfurization of a liquid hydrocarbon feed in a reactor having a reactor volume in the presence of a catalyst to produce a product stream comprising the steps of: measuring a carbazoles content of a plurality of liquid hydrocarbon feeds that are produced from distilling a plurality of initial liquid hydrocarbon feeds; generating a database of the plurality of liquid hydrocarbon feeds comprising their respective measured carbazoles contents; selecting a first liquid hydrocarbon feed for introduction into the reactor, wherein the first liquid hydrocarbon feed is selected from the generated database; selecting a desired sulfur content of a first product stream produced in the reactor from the first liquid hydrocarbon feed; calculating a reaction order for the first liquid hydrocarbon feed based on the measured carbazoles content of the first liquid hydrocarbon, wherein the step of calculating the reaction order comprises the step of determining a highest measured carbazoles content in the database and the reaction order of the first liquid hydrocarbon feed is calculated using the following equation: n = 1 + N carbazoles N carbazoles − max, where n is the reaction order, N carbazoles equals the carbazoles content of the first liquid hydrocarbon feed, and N carbazoles-max equals the highest measured carbazoles content in the database; and calculating an operating severity index based on the calculated reaction order, wherein the operating severity index comprises an operating temperature of the reactor to yield the first product stream with the desired sulfur content from the first liquid hydrocarbon feed, wherein the operating severity index is calculated using the following equations: k = LHSV ∗ S Pr ⁢ oduct 1 − n − S Feed 1 − n n − 1 k = A ∗ exp − E a R ∗ T ∗ HPP b ∗ Catage ∗ c and the calculated severity index is used in a subsequent step of hydrodesulfurization, wherein LHSV is a liquid hourly space velocity, and n equals the reaction order of the first liquid hydrocarbon feed, S Feed equals sulfur content of the first liquid hydrocarbon feed; S Product comprises the desired sulfur content of the first product stream; k is the nth order reaction rate constant, HPP is the hydrogen partial pressure, Catage is the catalyst age, A is the frequency factor, [ E a] is the activation energy, b is the hydrogen partial pressure dependency factor, c is the catalyst deactivation factor, R is the universal rate constant and T is the temperature of the reactor. measuring a carbazoles content of a plurality of liquid hydrocarbon feeds that are produced from distilling a plurality of initial liquid hydrocarbon feeds; generating a database of the plurality of liquid hydrocarbon feeds comprising their respective measured carbazoles contents; selecting a first liquid hydrocarbon feed for introduction into the reactor, wherein the first liquid hydrocarbon feed is selected from the generated database; selecting a desired sulfur content of a first product stream produced in the reactor from the first liquid hydrocarbon feed; calculating a reaction order for the first liquid hydrocarbon feed based on the measured carbazoles content of the first liquid hydrocarbon, wherein the step of calculating the reaction order comprises the step of determining a highest measured carbazoles content in the database and the reaction order of the first liquid hydrocarbon feed is calculated using the following equation: n = 1 + N carbazoles N carbazoles − max, where n is the reaction order, N carbazoles equals the carbazoles content of the first liquid hydrocarbon feed, and N carbazoles-max equals the highest measured carbazoles content in the database; and calculating an operating severity index based on the calculated reaction order, wherein the operating severity index comprises an operating temperature of the reactor to yield the first product stream with the desired sulfur content from the first liquid hydrocarbon feed, wherein the operating severity index is calculated using the following equations: k = LHSV ∗ S Pr ⁢ oduct 1 − n − S Feed 1 − n n − 1 k = A ∗ exp − E a R ∗ T ∗ HPP b ∗ Catage ∗ c and the calculated severity index is used in a subsequent step of hydrodesulfurization, wherein LHSV is a liquid hourly space velocity, and n equals the reaction order of the first liquid hydrocarbon feed, S Feed equals sulfur content of the first liquid hydrocarbon feed; S Product comprises the desired sulfur content of the first product stream; k is the nth order reaction rate constant, HPP is the hydrogen partial pressure, Catage is the catalyst age, A is the frequency factor, [ E a] is the activation energy, b is the hydrogen partial pressure dependency factor, c is the catalyst deactivation factor, R is the universal rate constant and T is the temperature of the reactor.