A process for removing sulfur compounds from a hydrocarbon stream, the process comprising the steps of: (a) introducing a reaction mixture into a reaction zone, wherein the reaction mixture comprises a mixture of the hydrocarbon stream and a water stream, wherein the hydrocarbon stream contains sulfur compounds; (b) subjecting the reaction mixture to operating conditions that are at or exceed the supercritical conditions of water, such that at least a portion of hydrocarbons in the reaction mixture undergo cracking to form an upgraded mixture, wherein at least a portion of the sulfur compounds are converted to hydrogen sulfide and thiol compounds, and wherein the reaction zone is essentially free of an externally-provided catalyst and externally-provided alkaline solutions; (c) cooling the upgraded mixture to a first cooling temperature that is below the critical temperature of water to form a cooled upgraded-mixture, the cooled upgraded-mixture defining an oil phase and an aqueous phase; (d) mixing an alkaline solution with the cooled upgraded-mixture in an extraction zone such that a substantial portion of the thiol compounds are extracted from the oil phase into the aqueous phase, the alkaline solution comprising an alkali salt and water; (e) separating the cooled upgraded-mixture into a gas stream and an upgraded liquid stream, wherein the gas stream contains a substantial portion of the hydrogen sulfide; and (f) separating the upgraded liquid stream into upgraded oil and recovered water, wherein the upgraded oil has reduced amounts of asphaltene, sulfur, nitrogen or metal containing substances and an increased API gravity as compared to the hydrocarbon stream and the recovered water includes water and a transformed thiol compound. (a) introducing a reaction mixture into a reaction zone, wherein the reaction mixture comprises a mixture of the hydrocarbon stream and a water stream, wherein the hydrocarbon stream contains sulfur compounds; (b) subjecting the reaction mixture to operating conditions that are at or exceed the supercritical conditions of water, such that at least a portion of hydrocarbons in the reaction mixture undergo cracking to form an upgraded mixture, wherein at least a portion of the sulfur compounds are converted to hydrogen sulfide and thiol compounds, and wherein the reaction zone is essentially free of an externally-provided catalyst and externally-provided alkaline solutions; (c) cooling the upgraded mixture to a first cooling temperature that is below the critical temperature of water to form a cooled upgraded-mixture, the cooled upgraded-mixture defining an oil phase and an aqueous phase; (d) mixing an alkaline solution with the cooled upgraded-mixture in an extraction zone such that a substantial portion of the thiol compounds are extracted from the oil phase into the aqueous phase, the alkaline solution comprising an alkali salt and water; (e) separating the cooled upgraded-mixture into a gas stream and an upgraded liquid stream, wherein the gas stream contains a substantial portion of the hydrogen sulfide; and (f) separating the upgraded liquid stream into upgraded oil and recovered water, wherein the upgraded oil has reduced amounts of asphaltene, sulfur, nitrogen or metal containing substances and an increased API gravity as compared to the hydrocarbon stream and the recovered water includes water and a transformed thiol compound.