A fuel oxygen reduction unit for an engine is provided. The fuel oxygen reduction unit includes an inlet fuel line; a stripping gas source; a contactor selectively in fluid communication with the stripping gas source, the inlet fuel line, or both to form a fuel/gas mixture; and a separator that receives the fuel/gas mixture, the separator configured to separate the fuel/gas mixture into an outlet stripping gas flow and an outlet fuel flow; wherein a flow of stripping gas passes through the fuel oxygen reduction unit a single time.