A process and system for upgrading an organic feedstock including providing an organic feedstock and water mixture, feeding the mixture into a high-rate, hydrothermal reactor, wherein the mixture is rapidly heated, subjected to heat, pressure, and turbulent flow, maintaining the heat and pressure of the mixture for a residence time of less than three minutes to cause the organic components of the mixture to undergo conversion reactions resulting in increased yields of distillate fuels, higher-quality kerosene and diesel fuels, and the formation of high octane naphtha compounds. Hydrocarbon products are cooled at a rate sufficient to inhibit additional reaction and recover of process heat, and depressurizing the hydrocarbon products, and separating the hydrocarbon products for further processing. The process and system can include devices to convert olefinic hydrocarbons into paraffinic hydrocarbons and convert olefinic byproduct gas to additional high-octane naphtha and/or heavier hydrocarbons by one of hydrogenation, alkylation, or oligomerization.