A process for upgrading heavy oil in an environment free of an externally supplied catalyst or externally supplied hydrogen source, the process comprising the steps of: combining heavy oil with a water feed in a mixing zone to form a heavy oil/water mixture, wherein the temperature of the heavy oil/water mixture does not exceed 150 degrees C, the mixing zone comprising an ultrasonic wave generator; subjecting the heavy oil/water mixture to ultrasonic wave energy to create a submicromulsion, wherein the ultrasonic wave generator generates ultrasonic waves at a frequency in a range from 10 to 50 kHz, the submicromulsion having a residence time within the mixing zone in the range of 10 to 120 minutes; pumping the submicromulsion through a pre-heating zone using a high pressure pump, wherein the high pressure pump increases the pressure of the submicromulsion to a target pressure at or above the critical pressure of water; heating the submicromulsion to a first target temperature, to create a pre-heated submicromulsion, the first target temperature being in the range of 150° C to 350° C; feeding the pre-heated submicromulsion into a reaction zone; heating the pre-heated submicromulsion within the reaction zone to a second target temperature that is at or above the critical temperature of water, such that at least a portion of hydrocarbons in the pre-heated submicromulsion undergo cracking to create a hot adapted-mixture, the reaction zone including a main reactor having an interior, the main reactor operable to withstand temperatures and pressures in excess of the critical temperature and critical pressure of water, the reaction zone being essentially free of an externally-provided catalyst and essentially free of an externally-provided hydrogen source; removing the hot adapted-mixture from the reaction zone and cooling the hot adapted-mixture to form a cooled adapted-mixture; and separating the cooled adapted-mixture to create upgraded oil and recovered water, wherein the upgraded oil is an upgraded heavy oil having reduced amounts of asphaltene, sulfur, nitrogen or metal containing substances as compared to the heavy oil. combining heavy oil with a water feed in a mixing zone to form a heavy oil/water mixture, wherein the temperature of the heavy oil/water mixture does not exceed 150 degrees C, the mixing zone comprising an ultrasonic wave generator; subjecting the heavy oil/water mixture to ultrasonic wave energy to create a submicromulsion, wherein the ultrasonic wave generator generates ultrasonic waves at a frequency in a range from 10 to 50 kHz, the submicromulsion having a residence time within the mixing zone in the range of 10 to 120 minutes; pumping the submicromulsion through a pre-heating zone using a high pressure pump, wherein the high pressure pump increases the pressure of the submicromulsion to a target pressure at or above the critical pressure of water; heating the submicromulsion to a first target temperature, to create a pre-heated submicromulsion, the first target temperature being in the range of 150° C to 350° C; feeding the pre-heated submicromulsion into a reaction zone; heating the pre-heated submicromulsion within the reaction zone to a second target temperature that is at or above the critical temperature of water, such that at least a portion of hydrocarbons in the pre-heated submicromulsion undergo cracking to create a hot adapted-mixture, the reaction zone including a main reactor having an interior, the main reactor operable to withstand temperatures and pressures in excess of the critical temperature and critical pressure of water, the reaction zone being essentially free of an externally-provided catalyst and essentially free of an externally-provided hydrogen source; removing the hot adapted-mixture from the reaction zone and cooling the hot adapted-mixture to form a cooled adapted-mixture; and separating the cooled adapted-mixture to create upgraded oil and recovered water, wherein the upgraded oil is an upgraded heavy oil having reduced amounts of asphaltene, sulfur, nitrogen or metal containing substances as compared to the heavy oil.