Abstract: Disclosed is a truck air foil having upper and lower elongated generally rectangular panels hinged one to the other along opposed edges. A bracket on the forward face of the cargo box pivotally mounts the upper edge of the upper panel while the lower edge of the lower panel is vertically adjustably mounted whereby the angle of attack or both the upper and lower panels is adjustable. A panel, arcuate in cross section, forms a transition surface between the upper panel and the top of the cargo box to reduce air separation from the top surface of the cargo box and minimize drag. In another form, triangular panels are disposed vertically along the lower panel to divide and deflect the air stream laterally toward the opposite sides of the truck air foil likewise to minimize air separation and drag along the sides of the truck.