Bunkering on Ships: How Bunkering Operations Work

Bunkering is the supply of fuel to a ship for its own engines, boilers and generators. Bunkering operations are high-risk routine jobs: one overflow means an oil spill, and one short delivery can cost thousands of dollars. This guide covers bunkering types, the step-by-step procedure, crew duties, quantity measurement, sampling, the Bunker Delivery Note and inspections.

What Is Bunkering on Ships?

Bunkering is the transfer of fuel into a ship’s bunker tanks, usually from a bunker barge, a road tanker or a shore pipeline. The fuel is for the ship’s own use, not cargo.

The word comes from the coal bunkers of steamships, the compartments where coal was stored. Today the “bunkers” are fuel tanks, and the fuel itself is also called bunkers.

The scale is large. Singapore, the world’s biggest bunkering port, sold a record 56.77 million tonnes of marine fuel in 2025. How much a ship needs depends on its size and speed, as shown in how much fuel cargo ships use.

What Are the Types of Bunkering?

The main types of bunkering are barge-to-ship, truck-to-ship and shore pipeline bunkering. Barge delivery is the most common for ocean-going ships, at berth or at anchor.

Type	How it works	Typical use
Barge-to-ship (ex-barge)	A bunker tanker or barge moors alongside and pumps fuel through hoses	Most ocean-going ships, at anchor or at berth
Truck-to-ship (ex-truck)	Road tankers on the quay pump fuel through hoses	Small volumes, ferries, tugs, ports without barges
Pipeline (ex-pipe)	Fuel flows from shore tanks through a fixed line at the berth	Terminals, ferry berths, tankers at their loading berth
Offshore bunkering	A bunker tanker supplies the ship outside port limits	Ships avoiding port calls, offshore support
LNG bunkering	Cryogenic transfer by bunker vessel, truck or terminal	LNG-fuelled ships

LNG is a separate operation with its own rules and equipment. See LNG bunkering for the procedure and the LNG bunkering vessels page for the ships that deliver it.

Debunkering is the reverse: pumping fuel out of a ship, usually after an off-spec delivery or before a dry-dock or sale.

What Fuels Are Bunkered?

Ships bunker very low sulphur fuel oil (VLSFO), high sulphur fuel oil (HSFO) with scrubbers, marine gas oil (MGO), LNG and biofuel blends. Each fuel needs its own tanks and handling.

• VLSFO: up to 0.50% sulphur, the global limit since 1 January 2020.
• HSFO: above 0.50% sulphur, allowed only with an approved exhaust gas cleaning system (scrubber).
• MGO / ULSFO: up to 0.10% sulphur, required inside Emission Control Areas (ECAs).
• LNG: for gas-fuelled ships; Singapore sold 571,400 t in 2025.
• Biofuel blends: usually FAME blended into VLSFO; Singapore sales rose more than 54% in 2025.

Sulphur limits come from MARPOL Annex VI, explained in MARPOL. Fuel quality is specified by ISO 8217. The wider fuel choice is covered in what fuel cargo ships use.

How Does a Bunkering Operation Work?

A bunkering operation runs from planning and a checklist through soundings, hose connection, a slow start, bulk transfer and topping off. It ends with closing soundings, samples and the signed Bunker Delivery Note.

1. Bunker plan: the chief engineer plans which tanks receive which grade, the maximum filling level and the order of filling.
2. Tank preparation: remaining fuel is transferred so new fuel goes into empty tanks where possible, avoiding commingling.
3. Pre-bunkering meeting: the plan, duties, communication and emergency stop signals are agreed with the crew and the barge.
4. Checklist: ship and supplier complete the bunker safety checklist together.
5. Opening soundings: ship’s tanks and barge tanks are sounded, with temperatures recorded, before any fuel moves.
6. Hose connection and sampler: the hose is connected and bolted, and a drip sampler is fitted at the ship’s manifold.
7. Slow start: pumping starts at a low rate to confirm fuel is reaching the right tank and there are no leaks.
8. Bulk transfer: the rate rises to the agreed figure while tanks are sounded at regular intervals.
9. Topping off: the barge slows the rate as each tank nears its limit, and the ship changes over tanks.
10. Completion: hoses are blown through, closing soundings are taken, samples are sealed and the BDN is signed.

Bunkering is recorded in the Oil Record Book Part I and in the engine logbook.

Who Does What During Bunkering?

The chief engineer is the person in charge of bunkering, with the master giving final approval. Engineers handle tanks, valves and soundings, while the duty deck officer looks after moorings, scuppers and safety on deck.

Role	Main duties
Master	Approves the operation, checks weather and moorings, informs port authorities if required
Chief engineer	Person in charge: bunker plan, pre-bunkering meeting, checklist, signs the BDN and receipts
Second engineer	Checks tank valves and lines, supervises soundings, assists with quantity calculation
Third or fourth engineer	Prepares the fuel system, vents and sounding pipes; records soundings before, during and after
Duty deck officer	Moorings of ship and barge, scuppers plugged, warning signs, fire hoses and SOPEP gear ready
Motorman or oiler	Sounds tanks at set intervals, watches the manifold, hose and pressure
Barge person in charge	Runs the supplier’s pumps, rate changes and barge soundings

In US waters, the person in charge also signs a Declaration of Inspection before the transfer starts. Ranks and titles are explained in shipboard organization and ranks, and third engineer duties covers that role in more detail.

What Is on a Bunkering Checklist?

A bunkering checklist confirms that hoses, tanks, valves, communication, moorings and spill equipment are ready before fuel moves. It is completed jointly by the ship and the supplier.

• Bunker hoses in good condition, correctly rigged and fully bolted at the flanges.
• Drip trays in place under the manifold, and scuppers plugged.
• Receiving tank valves open and other tank valves closed.
• Tank capacities and maximum filling levels known to everyone involved.
• Overflow tank empty and its alarm tested.
• Communication channel and emergency stop signal agreed with the barge.
• Pumping rate and pressure limits agreed.
• SOPEP equipment, absorbents and fire hoses ready.
• No smoking or naked flames, and accommodation doors and vents closed.
• Moorings of ship and barge checked, and weather limits agreed.

How Is Bunker Quantity Measured?

Fuel is delivered by volume but sold by weight, so the volume measured in the tanks is corrected to 15°C and multiplied by the density. Errors in temperature, density or soundings directly change the tonnes paid for.

1. Sound or ullage each tank and read the volume from the tank calibration tables, corrected for trim and list.
2. Measure the temperature and convert the observed volume to volume at 15°C using a volume correction factor (ASTM Table 54B).
3. Multiply by density at 15°C, minus 0.0011 for the weight in air, to get metric tonnes.

The cappuccino effect is air blown into the fuel to make it foam. Foamy fuel looks like more volume in the barge tanks, so the ship pays for air. Watch for bubbles in soundings and a rising level after pumping stops.

Mass flow meters remove most of this argument. Singapore made them mandatory for marine fuel oil deliveries from 1 January 2017. The printed metering ticket then becomes the basis for the BDN.

How Are Bunker Samples Taken?

Bunker samples are taken continuously throughout delivery by a drip sampler at the receiving ship’s manifold, then split into sealed bottles. The MARPOL sample must be kept on board for at least 12 months.

• MARPOL sample: required by MARPOL Annex VI Regulation 18, at least 400 ml, retained on board for at least 12 months.
• Ship’s retained sample: kept for any quality claim.
• Supplier’s sample: given to the barge.
• Laboratory sample: sent ashore for ISO 8217 testing before the fuel is used.
• Surveyor’s sample: if a bunker surveyor attends.

Adjust the needle valve so the sample bottle fills evenly from start to finish. Seal numbers go on the labels and the BDN.

What Is a Bunker Delivery Note?

A Bunker Delivery Note (BDN) is the supplier’s signed record of the fuel delivered, required by MARPOL Annex VI Regulation 18. It must be kept on board for three years.

The BDN shows the receiving ship, port, date, supplier, product, quantity in tonnes, density at 15°C and sulphur content. The supplier also declares that the fuel meets the applicable sulphur limit and Regulation 18 quality requirements.

Do not sign a BDN before delivery is complete and the quantity is agreed. If figures differ, sign with a remark and issue a letter of protest.

How Do You Avoid Fuel Compatibility Problems?

Avoid mixing new fuel with fuel already on board. When mixing cannot be avoided, run a compatibility test first, because incompatible fuels can form sludge that blocks filters and purifiers.

A spot test on board gives a quick answer, and the lab analysis confirms stability later. VLSFO blends vary widely between suppliers, so segregation matters more than it did with HSFO.

What Causes Oil Spills During Bunkering?

Most bunkering spills come from tank overflows, burst or badly connected hoses, open valves to the wrong tank and poor communication with the barge. Nearly all are preventable with a sound plan and close watch on soundings.

• Overflow: a tank filled past its limit, often during topping off.
• Hose or flange failure: worn hoses, missing bolts or excess pressure.
• Wrong valve line-up: fuel going to a full tank or out of an open vent.
• Communication failure: the barge not slowing or stopping when asked.

If a spill happens, stop pumping, contain oil on deck and follow the ship’s SOPEP, which MARPOL Annex I requires. Report it as the SOPEP and local rules demand.

How Are Bunker Disputes Handled?

Bunker disputes usually concern short delivery or off-spec quality. The ship’s best defence is good records: soundings, temperatures, samples, the BDN and letters of protest issued at the time.

• Quantity claims: compare ship and barge figures, check the cappuccino effect and record everything before signing.
• Quality claims: rely on the sealed drip samples and the lab report against ISO 8217.
• Independent survey: owners often appoint a bunker surveyor to witness soundings, sampling and paperwork.

What Do Inspectors Check on Bunkering?

Port State control officers check BDNs, MARPOL samples, Oil Record Book entries, sulphur compliance and the ship’s bunkering procedures. Missing BDNs or samples are common deficiencies.

• BDNs: on board for three years, matching the ORB entries.
• MARPOL samples: sealed, labelled and kept for at least 12 months.
• Oil Record Book Part I: bunkering entries with dates, grades and quantities.
• Sulphur compliance: fuel sulphur against the 0.50% and ECA 0.10% limits, plus changeover records.
• Procedures and drills: bunkering procedures and spill drills in the safety management system under the ISM Code.

See port State control MoUs for how inspections are organised.

Related Topics

• How Bunker Trading Works
• Bunker Adjustment Factor (BAF)
• Bio-LNG as a Marine Fuel

Frequently Asked Questions