Hydro Pneumatic Suspension is a kind of automotive suspension system that was invented by Citroen. All the Citroen cars are fitted with it and also used by other manufacturers under licence. The main aim of this system is to offer superior ride quality by providing dynamic, sensitive as well as high capacity suspension. This system uses nitrogen reservoir with a variable volume that results in a spring through the characteristics of non linear force deflection. Thus, this method will not have eigen frequencies as well as associated dynamic inabilities that are found in the conventional suspension systems. The nitrogen spring reservoir is activated through the hydraulic fluid found inside the suspension cylinder. Here the nitrogen gas is used as spring medium and it is six times stronger than the steel. Hence, self leveling helped the vehicle to cope with the resultant extraordinary suppleness. This system actually uses a camshaft or belt driven pumps from the engine to pressurize the special hydraulic fluid which powers brakes, suspension, power steering, etc. In order to provide the driver with extra clearance while travelling in rough terrain, this system comes with driver variable ride height.