In the primary distribution segment of the oil and gas industry, marine liners play a major role in moving petroleum products across the globe in an economical and efficient manner. Across continental product supplies, coastal movements are the preferred choice of oil organizations as the mode of transportation. These massive tanker vessels require huge quantities of fuel oil to propel their engines. This fuel for vessels is as per the specification prescribed by the vessel operator. Generally, Low Sulfur Heavy Fuel oil (LSFO) is commonly used as fuel for ships though other fuel oils are also used. The process of filling the fuel tanks of the vessels is known as bunkering. Though it appears to be a simple activity, it has a very detailed operating procedure which has to be strictly followed keeping in view the safety and environmental factors.

Before we get into details of the standard operating procedure relating to bunkering, let us briefly see what are the different types of vessels available in the market that are used for fuel transportation across globe.

Clean Vs Dirty tankers

The first tanker set sail about 120 years ago in 1886. Since then oil transportation has exponentially grown both in terms of number of vessels and the volume of oil transported worldwide. It is interesting to note that nearly half the world's seaborne trade constitutes of crude oil or petroleum products. Compared to the total volume of goods moved through marine transportation, the volume of crude almost doubled from 1952 to 2002. Tankers move approximately 2 billion tons of oil every year. In this, about three fourth of this volume is crude and one fourth is refined products. The largest tankers carry up to 4 million barrels of crude oil, which translates to roughly more than 600 million liters. Refined products like fuel oil, naphtha, jet fuel, and lubricating oils travel in smaller tankers but in separate compartments for different products. Hence, multiple products are moved in a vessel for the intended destination.

Crude tankers move large quantities of unrefined crude oil from its point of extraction to refineries. Product tankers, generally smaller, are designed to move petroleum products, petroleum specialties and petrochemicals from refineries to points near consuming markets. These two types of tankers are also referred to as either "clean" or "dirty". Clean tankers carry refined petroleum products such as gasoline, kerosene, jet fuels and chemicals while dirty vessels transport products such as heavy fuel oils or crude oil. Larger tankers usually only carry crude oil.

Value for investment

Oil tankers are not only used for transportation but also as floating storage units. This is preferably done with ships close to the end of their days in duty. On average, an oil tanker has a lifetime of about 25 years, which does not seem to be very long considering the investment of around 40 Million USD for small and 120 Million USD for large tankers. On the other hand, the value of a single load of such a giant tanker easily surpasses the value of the ship.


Oil tankers which are being used nowadays are enormous vessels. ULCCs (ultra large crude carriers) are supertankers that can carry more than 330,000 tons of cargo. Such huge supertankers need very large ports to load and unload their cargo and many ports are offshore terminals served by underwater oil pipelines. Additionally, super tankers cannot pass through the Panama and/or Suez channel, but they need to circumnavigate the capes of South Africa and South America. However, the closure of the Suez Channel in 1967–75 was one of the factors that encouraged the building of these giant ships as the smaller vessels were forced to take longer route which was unviable.

How is bunkering done?

Assessment of fuel requirements for oil vessels is similar to the other vehicles like cars and trucks. The concept of mileage of vehicles is similar and upon estimating the nautical miles of the proposed voyage and based on the fuel required to travel per nautical mile, total bunkering required is arrived. Once the quantity of fuel and lubricants is estimated, approval from the vessel captain is obtained by the person-in-charge for running the main propelling engines and auxiliary engines on board. The quantities of fuel and lubricants along with the specifications are ordered to the bunkering supplier who will arrange for the supplies at the stated port of call. Since huge quantities of fuel are ordered which entail significant costs, one has to take care of key commercial details such as prices, taxes, additional charges, if any, before deciding the port of call. Also, facilities available for bunkering should be taken into account before arriving at this decision.

Bunkering is an interesting operation though it is a very specialized task to perform particularly when it comes to large carriers like ULCC. Once the supplier and port of call is decided, the vessel has to be prepared for bunkering operation. The engineer who is responsible for looking after the fuel position of the vessel, has to assess the opening stocks of fuel present in each of the fuel tanks of the vessel. For huge vessels, fuel tanks are considerably big and accurate assessment of the fuel present, the sequence in which the tanks are to be filled and the amount of fuel to be loaded on each tank has to be carried out. This helps to maintain the balance of the ship. This is called a bunkering plan and it has to be approved by the captain of the vessel. Utmost care and attention to detail from a safety perspective has to be taken into consideration to ensure complete safety of the vessel and environment.

Based on the bunkering plan, arrangements are made by the bunkering supplier. As per the rules of the International Maritime Organization (IMO), a shipboard oil pollution emergency plan has to be prepared and put into effect during a bunkering operation. It is known as SOPEP and this details what are the equipment & accessories needed to manage in case of oil spill incident during bunkering operations.

Delivery Note and Invoices for bunkering fuel

Once bunkering is done, a delivery note is prepared with the quantity of fuel supplied and has to be approved by the vessel engineer and captain as an acknowledgement of receipt of bunkering. Since petroleum products expand as per the temperature, detailed calculation of actual quantity supplied in volume and weight after due temperature correction (usually to 15 deg C) is arrived at. Invoice is created for the quantity either in volume or in weight as per the terms of the supply contract. It is also a business practice to keep a sample of the fuel delivered for future reference by the vessel operators.