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What is bunker? What are the different types of bunkers?

Updated: Feb 4, 2021

Bunker is liquid fuel that is burned to generate heat and then used to power a ship's engine. The reason why it is called "bunker" (which is also a term used to refer to an underground shelter) is because when ships were powered by coal, the storage container or compartment on the ship was called a "bunker". Today we still keep the name, as the process of bunkering fuels and powers the vessels.

There are several types of bunker fuel. In this blog, we will talk about the most common fuels we broker daily.

1) Heavy fuel (mainly VLSFO RMG380CST 0.5% max sulfur)

This is the fuel used to propel the engines, and power the ship. We recently published another post explaining the different specifications of the fuel - check here for details.

There are different grades of heavy fuel. The most common is RMG380CST.

To offer a brief explanation without going into too much detail, the first 3 letters generally start with RMA, RMB, RMD, RME and indicate the different specification required. 380CST refers to the viscosity of the product (resistance or consistency of a fluid) . The smaller the number is (for example 10CST / 30CST) the thinner or more liquified the resistance/ consistency is, and the bigger the number is, the thicker the viscosity (e.g. 500CST / 700CST).

Heavy fuel has different grades of sulfur. VLSFO (very-low sulfur fuel oil) has 0.5% max sulfur and is compliant with the new regulation of global caps that came into effect in 2020. Prior to that, ships could burn up to 3.5% max sulfur.

Some ships are equipped with a scrubber (a self-purifying system able to burn, reduce and eliminate sulfur in HSFO, which is high sulfur fuel oil with a max of 3.5%). A ship with a scrubber can burn RMG380CST 3.5% and reduce the sulfur released into the atmosphere from 3.5% max to 0.5% max.

2) MGO (Marine Gas Oil)

MGO is similar to heavy fuel in that there are different grades of sulfur. Some are 0.5% max sulfur, but most are generally 0.1% max and are called LSMGO (Low Sulfur Marine Gas Oil). The product is transparent and clear, without any colour.

A slight variation to this is MDO (Marine Diesel Oil) which is often a blend of heavy fuel, and MGO. As you may imagine, the level of clarity is lower, and the specification is also less purified.

Depending on the country, this product can be referred to in many different ways, such as MGO, MDO, LSMGO, DML, Diesel. If you are not sure which product is being referred to, just ask for a specification to be sent, and/or ask which specification is guaranteed (such as ISO 8217 2010 or 2012 specs). This will help to pinpoint the correct product.

3) Lubricants

This is the oil that is used to lubricate the engine, so it will have to be matched with the heavy fuel that is used.

If the viscosity of the heavy fuel is lower than 30CST, or higher than 380CST, the lubricant that needs to be used can be quite different.

The selling price also varies. Bunker is mostly sold at USD per metric ton price, whilst lubricants are sold in drums in lots (or sets) of 206/208 litres, or by pallet which is a higher quantity (4-6 drums combined).

We hope you have found this blog useful. As always, if you have any questions or would like to discuss this further please do not hesitate to contact us at

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