MFO

Marine fuels are traditionally classified according to their kinematic viscosity. This is a valid criterion for oil quality as long as the oil is produced by atmospheric distillation only. Today, almost all marine fuels are based on fractions from more advanced refinery processes and the viscosity itself says little about the oil's quality as fuel. Despite this, marine fuels are still quoted on the international bunker markets with their maximum viscosity set by ISO 8217 as marine engines are designed to use different viscosities of fuel. The density is also an important parameter for fuel oils since marine fuels are purified before use to remove water and dirt. Therefore, the oil must have a density which is sufficiently different from water.

Marine fuels are classified using the “Bunker ABC”:

1. Bunker A corresponds to the distillate fuel oil No. 2
2. Bunker B is a No. 4 or No. 5 fuel oil
3. Bunker C corresponds to the residual fuel oil No. 6
No. 6 is the most common oil, that's why "bunker fuel" is often used as a synonym for the No. 6 residual fuel oil which requires heating before the oil can be pumped. No. 5 fuel oil is also called “navy special”. No. 5 or No. 6 also furnace fuel oil (FFO).

In the maritime field another classification is used:

1. MGO (Marine Gas Oil): a distillate fuel oil (No. 2, Bunker A)
2. MDO (Marine Diesel Oil): a blend of MGO and HFO
3. IFO (Intermediate Fuel Oil): a blend of MGO and HFO, with less gasoil than MDO
4. MFO (Medium Fuel Oil): a blend of MGO and HFO, with less gasoil than IFO
5. HFO (Heavy Fuel Oil): a residual fuel oil (No. 6, Bunker C)
No. 6 is the most common oil, that's why "bunker fuel" is often used as a synonym for the No. 6 residual fuel oil which requires heating before the oil can be pumped. No. 5 fuel oil is also called “navy special”. No. 5 or No. 6 also furnace fuel oil (FFO).