Abstract: Methods and systems for reducing sulfur content in crude oil are provided. The methods and systems apply a first alkaline aqueous solution to crude oil to produce alkaline-treated crude oil, apply an acid aqueous solution to the alkaline-treated crude oil to produce acid-treated crude oil, apply a second alkaline aqueous solution to the acid-treated crude oil to produce neutralized crude oil; and separate residual water that contains sulfur from the neutralized crude oil to produce treated crude oil that has less sulfur content than the crude oil before the treatment.