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Bunker Fuel Terminology

Bunker Fuel Definition: there are two basic types of marine fuels - distillate and residual. A third type is a mixture of these two, commonly called "intermediate".  Distillate fuel is composed of petroleum fractions of crude oil that are separated in a refinery by a boiling or "distillation" process. Residual fuel or "residuum"  is the fraction that did not boil, sometimes referred to as "tar" or "petroleum pitch". Fuel for marine use in engines and boilers has the following types and grades:

Fuel Type & Fuel Grades Common Industry Name

  • Distillate DMX, DMA, DMB, DMC Gas Oil or Marine Gas Oil
  • Intermediate IFO 180 380 Marine Diesel Fuel or
  • Intermediate Fuel Oil (IFO)
  • Residual RMA-RML Fuel Oil or Residual Fuel Oil


Additionally, it is common for different suppliers to use their own in-house terminology as illustrated below.

Mobil          Chevron     Esso     Shell     Texaco
Motorship Fuel OilIntermediate Bunker Fuel (BF*)Bunker Fuel Oil (BFO)Marine Fuel Oil (MFO*)Interfuel (IF*)    
Light Marine Fuel Oil (LMFO)Intermediate Bunker Fuel (BF*)Intermediate Fuel (IF*)Marine Fuel Oil (MFO*)IF*
Marine Diesel Oil (MDO)    Marine Diesel Oil (MDO)Marine Diesel Oil (MDO)Marine Diesel Oil (MDF)Marine Diesel Oil (MDO)
Distillate Marine Diesel OilLight DieselLight Diesel Oil (LDO)Marine Diesel Fuel or Gas Oil (MDF/GO)Marine Distillate
Marine Gas Oil (MGO)    Gas Oil (GO)    Marine Gas Oil (MGO)    Gas Oil (GO)    Gas Oil (GO)    
Notes: * Denotes a specific grade, usually shown by viscosity of the grade in cSt at 50°C

To communicate effectively in a speciality field like "marine-fuels" it is necessary to be clear on the bunker fuel terminology used in this industry. Distillate fuels are commonly called "Gas Oil" or Marine Gas Oil; residual fuels are called Marine Fuel Oil or Residual Fuel Oil; and intermediate types are called "Marine Diesel Fuel", or Intermediate Fuel Oil (IFO). While the term "diesel fuel" for land based automobile and truck use is 100% distillate, in the marine industry Marine Diesel Fuel is the blend of distillate and residual oils (intermediate types). The 100% distillate type fuel in the marine industry is the Marine Gas Oil (implying that it was boiled into a gas, then condensed into a liquid).

Fuel Oil, or Residual Fuel Oil, refers to fuels that are primarily non-boiling fractions. Depending on the pressures and temperatures in refinery distillation processes, and the types of crude oils, slightly more or less gas oil that could be boiled off is left in the non-boiling fraction, creating different grades of Residual Fuel Oils. In other words, intermediate grades of fuel oil can be made directly in the distillation process or by blending with distillate. Another clarification that is necessary in this study involves the terms "recreational" versus "commercial" uses of marine vessels. The Environmental Protection Agency, EPA, has defined the terms "recreational marine engine" and "recreational vessel" in 40 CFR Part 94: Control of Emissions of Air Pollution from New CI Marine Engines >37 kW.


One common theme is that the world of commercial marine fuel supply is totally separate from the world of recreational marine fuels. Diesel fuel for marine applications depends on three things: engine used, cost, and availability. Commercial marine businesses have the higher volume and low-cost incentives to arrange deals with refiners to produce tailored marine fuels that are most cost effective for their engines. Commercial marine businesses arrange for fuels that involve less refining (leaving the sulphur in the fuel), and therefore lower cost than other diesel fuels, delivered by pipeline, boat or barge.

The product that is supplied as DMA is sometimes specially manufactured at local refineries with a higher sulphur content and lower price than land-based fuels rebranded for marine use. When that supply is short of demand, "Home-Heating Oil" (No 2 fuel oil) is used, provided the flash is above 60ª C, which it normally is. Similarly, DMC is sometimes supplied by local refineries from "cycle oil" (lower boiling point than No 2 fuels), and is sometimes blended in the supply terminal from DMA and residual fuel oils.  DMA is the common fuel for tugboats, fishing boats, crew boats, drilling rigs and ferry boats. Ocean-going ships that take residual fuel oil bunkers also take distillate fuels for use in auxiliary engines and sometimes for use in port. The common fuels are DMC, IFO-180 and IFO-380, depending on the specific engines in service. DMB is infrequently specified, and is not available in all ports. Where it is not available, DMA is supplied, sometimes in a barge that has transported DMC or IFO (hence, a "dirty" cargo hold that would contaminate DMA).

In contrast to commercial marine businesses, recreational boat owners have no volume leverage, and less cost-reduction incentives to arrange for special fuels. With the large overlap in boiling range with other distillate fuels, the sources of recreational marine fuels are often land-based fuels that can meet or exceed all specifications of the marine fuel.

Off-line Bunker Fuel

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