Bunker fuel is any fuel used on board a ship.

The most commonly used type is residual fuel oil bunker or Bunker C.

Grades of Bunker fuel

Bunker A - Gasoil range bunker fuel, typically called marine diesel (MDO) or marine gasoil (MGO).

Bunker B - Low viscosity Vac resid range bunker fuel. Typically cut with some lighter material (VGO) to reduce viscosity to the point that it will flow without heating.

Bunker C - The most common form of bunker. Comprised primarily of vac resid range material, with a high viscosity that requires heating in order to pump. Typically sold at several viscosity specifications: 180 centistoke, 380 centistoke or 460 centistoke, with 380 being the most common grade. The viscosities are measured at 50 degrees C, the typical heated temperature of the fuel.

In addition, the bunker fuel which can be used in the Sulfur Emissions Control Areas (SECAs)  must have a maximum sulfur content of 0.1% which require either using Bunker A or a Ultra Low Sulfur Fuel Oil (ULSFO).  SECAs currently include the Baltic Sea, the North Sea, the English Channel and the area up to 200 nautical miles off the North American coast plus a zone in the Caribbean.

From January 1st, 2020, bunker fuels used globally outside the SECA regions will be restricted to having a maximum sulfur content of 0.5% .

Alternative bunker fuels

A number of non-traditional fuels are being considered as alternatives in an effort to reduce sulfur emissions and increasingly to reduce CO2 emissions. These include:

• LNG - LNG has been adopted by some shipping companies to comply with lower sulfur emissions limits as a result of IMO 2020. LNG from green sources (bio-LNG, synthetic-LNG) is seen as a potential zero or negative CO2 fuel.  

• Hydrogen - Green hydrogen (from renewable power or biomass)  

• Ammonia - Green ammonia from green hydrogen or bio-methane

• Methanol - Bio-methanol or e-methanol