Some automobiles use transmission fluid as power steering fluid, while newer vehicles use synthetic-based hydraulic fluid that is specifically made for power steering use. The four main automatic transmission fluid types are Mercon, Dexron, Type F and ATF +4.
Most fluids used by power steering systems are made from synthetic oil or mineral oil with different additives to prevent corrosion, suppress foaming and improve lubrication in the steering gear and power steering pump. Japanese and European automobiles usually have their own specific requirements for power steering fluid. Vehicles from these countries may require high performance synthetic type fluids that adhere to DIN 51 524T3 and ISO 7308 standards.