Bunkering Operation

What is Bunker and Bunkering?

Bunker is simply the name given to the Fuel that is used to operate ships. Bunkering is the action of supplying a ship with bunkers. There are various types of Fuel Oil and within the Fuel Oils, there are many classifications, standards and grades.




In the maritime industry the following types of classifications are used for marine fuel oils:

  • MGO (Marine Gas 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/40°C 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.
  • MFO (Marine Fuel Oil) – same as HFO.
  • HFO (Heavy Fuel Oil) – Pure or nearly pure residual oil.

Standards and Classification

Marine fuels were traditionally classified after their kinematic viscosity. This is a mostly valid criteria for the quality of the oil as long as the oil is made only from atmospheric distillation. Today, almost all marine fuels are based on fractions from other more advanced refinery processes and the viscosity itself says little about the quality as fuel. CCAI and CII are two indices 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. The unit of viscosity used is the Centistoke 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/50°C
  • IFO 180 – Intermediate fuel oil with a maximum viscosity of 180 Centistokes/50°C
  • LS 380 – Low-sulphur (<1.5%) intermediate fuel oil with a maximum viscosity of 380 Centistokes/50°C
  • LS 180 – Low-sulphur (<1.5%) intermediate fuel oil with a maximum viscosity of 180 Centistokes/50°C
  • MDO – Marine Diesel Oil.
  • MGO – Marine Gasoil.

The density is also an important parameter for fuel oils since marine fuels are cleaned by centrifugal type separators before use to remove water and dirt from the oil. Since the separators use centrifugal force, the oil must have a density which is sufficiently different from water. Conventional type separators of purifier type  have a maximum density limit of 991 kg/m3/15°C with modern High Density type separators it’s possible to clean fuel oils with a maximum density of 1010 kg/m3/15°C.

The first British standard for fuel oil came in 1982. The latest standard is ISO 8217 from 2005. The ISO standard describe four qualities of distillate fuels and 10 qualities of residual fuels. Over the years the standards have become stricter on environmentally important parameters such as sulfur content. The latest standard also banned the adding of used lubricating oil (ULO).


The purpose of the pre-delivery document is to record agreement on the operational details of the transfer and to ensure safe transfer of the product. This document originates from the Gulf Energy’s representative and states the grade or grades with the nominated quantity. Ideally the grades will be expressed by reference to ISO 8217, which defines viscosity for residual fuel oil grades at 50 °C . Distillate grades, instead of being referenced as DMA or DMB may be referred to as marine gas oil or marine diesel.
Having established what is to be transferred, agreement has to be reached on the pumping rate acceptable to the receiving vessel to ensure safe transfer. The next aspect to be considered is witnessing of tanks by sounding or ullage . Agreement should be reached on the witnessing of a representative sample . The spill prevention transfer procedure must also be discussed and agreed. The key to this is communication and a checklist can be useful to ensure no points are missed.


The purpose of the Bunker Delivery Note (BDN or Bunker Delivery Receipt, BDR) is to record what has been transferred. MARPOL Annex VI requires the following details to be included:

  • Name and IMO Number of receiving ship.
  • Port.
  • Date of commencement of delivery.
  • Name, address, and telephone number of marine fuel oil supplier.
  • Product name(s).
  • Quantity in metric tons.
  • Density at 15°C, kg/ M3.
  • Sulphur content (%m/m).

In addition the BDN will include:

  • Temperature of product delivered.
  • Sample seal numbers.

As per The MARPOL BDN  Gulf Energy’s representative will be signing a declaration that the fuel oil is a blend of hydrocarbons derived from petroleum refining that

  • Meets applicable sulphur limits.
  • Is free from inorganic acid.
  • Does not include any added substance or chemical waste that.

-      Jeopardizes the safety of ships or adversely affects the performance of the machinery,

     -      Is harmful to personnel, or

     -      Contributes overall to additional air pollution.

Alternatively, in the case that the fuel oil is derived by methods other than petroleum refining, as well as meeting the above conditions it must not

  • Cause an engine to exceed the applicable NOx emission limit

Care should be taken before signing the BDN. For example, the bunkers should not be signed for in weight form, only for volume at observed temperature. The actual weight can only be calculated after a representative sample of the delivery has been tested for density. 

MARPOL Annex VI requires the BDN to be retained for at least 3 years from the date of issue.

Should there be any dispute in the quantity of bunkers delivered, the purchaser or his representative should issue a letter of protest, which is properly signed and stamped by both parties. The barge or fuel oil supplier as well as the ship owner or engine operator can use the letter of protest system.


 A few relevant points are detailed below:- 

  • The purchaser should obtain specification acceptance from the supplier.
  • Purchaser needs to advise ship’s staff what grade of fuel will be delivered and how transferred.
  • Fuels from different deliveries should be segregated as far as practical.
  • All receiving tanks need to be gauged prior to taking fuel.
  • No documents to be signed, unless relevant task has been witnessed.
  • All operation should be witnessed by the purchase’s representative.
  • Receiving vessel’s representative should sign all collected samples which was obtained during the supply operation.
  • Wherever possible always take fuel samples using a continuous drip method throughout the bunkering at the point of delivery on the receiving ship i.e. as close as practical to the hose connection.
  • At least four-five samples will be required for each barge/delivery/fuel grade :-
    a)  The official MARPOL sample which the Port State Control Officer (PSCO) may be required to be analyzed. Note the MARPOL sample must be a minimum of 400 ml and be retained for at least 12 months.
    b)  The receiving vessel’s retained sample.
    c)  A sample for laboratory analysis.
    d)  A sample for onboard analysis.
    e)  A sample for the supplier.
     f)  Note further samples may need to be provided for any retained bunker surveyors.
  • Ensure good records are kept throughout the bunkering.
  • Keep bunkering fuel samples for at least 12 months.
  • Use on-site tests to check all fuel on delivery for Viscosity, Density, Water, Stability, Pour Point and Salt.
  • Use a laboratory to check results in the event of any discrepancies being indicated by on-site test equipment.


Whatever the method of fuel oil delivery, the only way to determine the volume delivered to the recipient vessel is by taking a sounding or ullage of the Bunker Supply vessel’s tanks.


 The only method would be by soundings/ullaging of the shore fuel storage tanks at the beginning and end of delivery.

 The Chief Engineer or a member of  receiving ship’s staff should witness the gauging the shore tanks and establish if pipelines were empty or full before and after the bunkering. Sometime the only practical way is to appoint a surveyor who has access to the tank and who will be able to carry out the pipeline calculations. Sometimes volume meters are available .


Road Tankers deliveries occasionally take place. In general, these are usually related to distillates, with the fuel measured by a meter.


When making an accurate bunker fuel quantity determination, it is necessary to take the temperature of the bunkers both at the beginning and end of delivery so that volumes can be corrected back to the standard temperature of 15 °C . This applies to shore tanks, road tankers and also a barge delivery.


Bunker collected sample will form the basis of any discussion, debate or dispute resolution relating to the bunkering quality . The most economic means of obtaining a representative sample is by using a drip type sampler. In back to back tests performed by a major fuel bunkering services laboratory over an extended period, fuel oil samples obtained by drip samplers were identical to those from more expensive automatic fuel samplers.

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