Standards and classification

In the maritime field another type of classification is used for fuel oils:

• MGO (Marine gas oil) – roughly equivalent to No. 2 fuel oil, made from distillate only
• MDO (Marine diesel oil) – A blend of heavy gasoil that may contain very small amounts of black refinery feed stocks, but has a low viscosity up to 12 cSt so it need not be heated for use in internal combustion engines
• IFO (Intermediate fuel oil) A blend of gasoil and heavy fuel oil, with less gasoil than marine diesel oil
• HFO (Heavy fuel oil) – Pure or nearly pure residual oil, roughly equivalent to No. 6 fuel oil
• MFO (Marine fuel oil) – same as HFO (just another “naming”)

Marine diesel oil contains some heavy fuel oil, unlike regular diesels.

CCAI and CII are two indexes which describe the ignition quality of residual fuel oil, and CCAI is especially often calculated for marine fuels. Despite this, marine fuels are still quoted on the international bunker markets with their maximum viscosity (which is set by the ISO 8217 standard – see below) due to the fact that marine engines are designed to use different viscosities of fuel.^[6] The unit of viscosity used is the centistoke (cSt) and the fuels most frequently quoted are listed below in order of cost, the least expensive first.

• IFO 380 – Intermediate fuel oil with a maximum viscosity of 380 centistokes (<3.5% sulphur)
• IFO 180 – Intermediate fuel oil with a maximum viscosity of 180 centistokes (<3.5% sulphur)
• LS 380 – Low-sulphur (<1.0%) intermediate fuel oil with a maximum viscosity of 380 centistokes
• LS 180 – Low-sulphur (<1.0%) intermediate fuel oil with a maximum viscosity of 180 centistokes
• MDO – Marine diesel oil.
• MGO – Marine gasoil.
• LSMGO – Low-sulphur (<0.1%) Marine Gas Oil – The fuel is to be used in EU Ports and Anchorages. EU Sulphur directive 2005/33/EC
• ULSMGO – Ultra-Low-Sulphur Marine Gas Oil – referred to as Ultra-Low-Sulfur Diesel (sulphur 0.0015% max) in the US and Auto Gas Oil (sulphur 0.001% max) in the EU. Maximum sulphur allowable in US territories and territorial waters (inland, marine and automotive) and in the EU for inland use.

The density is also an important parameter for fuel oils since marine fuels are purified before use to remove water and dirt from the oil. Since the purifiers use centrifugal force, the oil must have a density which is sufficiently different from water. Older purifiers work with a fuel having a maximum of 991 kg/m3; with modern purifiers, it is also possible to purify oil with a density of 1010 kg/m3.