Abstract: A system for reducing the drag on a trailer comprises a series of air ducts mounted beneath the trailer which each have an intake located beneath the trailer. The duct is connected to a plurality of vertical pipes, each having vertically-spaced pipes air discharge holes. Movement of the trailer forces air to flow into the inlet, through the ducts and out the outlets. Preferably, the duct inlets face the front and the side of the trailer, and the ducting forces all inlet air into a common plenum, through a venturi and out through a series if outlets spaced about the rear surface of the trailer. A vortex generator may be used and a spoiler is fitted. The entire system is designed to be retrofitted to existing trailers without loss of cargo space.