D6 is also known as Residual Fuel Oil and is of high-viscosity. This particular fuel oil requires preheating to 220 – 260 Degrees Fahrenheit. D6 is mostly used for generators. D6 is a type of residual fuel, mainly used in power plants and larger ships. The fuel requires 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. In other parts of the world it has other names. Residual means the material remaining after the more valuable cuts of crude oil have boiled off. The residue may contain various undesirable impurities including 2 percent water and one-half percent mineral soil.

The unit of viscosity used is the Centistoke and the d6 fuel most frequently quoted are listed below in order of cost:

IFO 380 – Intermediate d6 fuel oil with a maximum viscosity of 380 Centistokes

IFO 180 – Intermediate d6 fuel oil with a maximum viscosity of 180 Centistokes

LS 380 – Low-sulphur (<1.5%) intermediate d6 fuel oil with a maximum viscosity of 380 Centistokes

LS 180 – Low-sulphur (<1.5%) intermediate d6 fuel oil with a maximum viscosity of 180 Centistokes

MDO – Marine diesel oil.

MGO – Marine gas oil.