Product tankers are characterised by having coated tanks to prevent corrosion from the refined products and to facilitate cleaning of the tanks. Especially for the transportation of ”clean products”, there are strict requirements that the tanks must be completely clean before a new product is loaded, because the products must have as high a degree of distillation as possible. Furthermore, to ensure as clean a product as possible, the oil companies often stipulate which type of products the tanker must recently have transported.