It is desirable to minimise all forms of trailing vortices from a moving vehicle, whether they are from turbulent form drag of a vehicle or from vortex drag. Wingtip vortices on aircraft can persist for relatively long times (of the order of several minutes after the passage of an aircraft) which can cause danger to other aircraft, in particular around airfields where time must be left between subsequent take-offs and/or landings on a given runway for such vortices to dissipate. According to a first aspect of the present invention, there is provided an active drag-reduction system having first (22) and second (24) fluid outlets located on a vehicle (10) adjacent to a low pressure (drag) region (12), wherein fluid ejected from the second fluid outlet (24) is at a higher pressure / ejection velocity than from the first fluid outlet (22). Turbulent and/or low pressure regions adjacent to vehicles are not uniform, but rather have a varying intensity. For instance, the centre of a region may have a lower pressure and/or more turbulent nature than the periphery of the region. In this way, therefore, the present invention allows the system of the present invention to inject relatively higher pressure air (or relatively higher speed air) into the relatively lower pressure / more turbulent part of the low pressure / turbulent region, and relatively lower pressure air (or relatively lower speed air) into the relatively higher pressure / less turbulent part of the low pressure / turbulent region, compared to each other.