Abstract: A process for reducing coke and coke precursor formation in supercritical water may include producing a supercritical water stream by heating and pressurizing a feed water, mixing the supercritical water stream with heated pressurized feed oil in a mixing device, to create a combined feed stream, feeding the combined feed stream into a supercritical water reactor to produce an upgraded product producing a cooled depressurized upgraded product, separating the cool depressurized product in a fractionator into a liquid hydrocarbon stream and a hydrocarbon vapor stream, condensing the hydrocarbon vapor stream with a cooling device to produce a light hydrocarbon water mixture and a separate gas product, recycling the light hydrocarbon mixture to mix with the feed water upstream of the supercritical reactor.