STP 65934US Diesel Oil Treatment: Used for diesel engines has been designed specifically for all diesel engines, providing essential additives found in premium quality diesel engine oils and when used between oil changes, will replace burnt out minerals and additives in the oil to reduce diesel operating costs. STP stands for Scientifically Treated Petroleum. Formed in 1954 in the United States the company has a strong history with motor racing that has allowed it to demonstrate the high quality nature of its products.