Sold per Gallon Email us for custom pricing email@example.com Or add this item as a quote to your cart and complete the quote checkout process. D6 230CST: is a type of residual fuel, mainly used in power plants and larger ships. The fuel is required to be preheated before it can be used. It is not possible to use it in smaller engines or vessels/vehicles where it is not possible to pre-heat it. D6 is its name in the USA. ... D6 fuel is used mostly for generators.