Bunkering is the supply of fuel to a ship for its own propulsion and machinery, and the name survives from the coal bunkers of steamships. Today it covers heavy fuel oil delivered by barge, road tanker deliveries in small ports, and LNG or methanol at a growing number of terminals.
It is also the moment a vessel’s compliance record begins. Every sulphur limit, every emissions calculation and every penalty a ship faces later is computed from figures created during a bunkering operation that usually takes a few hours.
Bunkering happens in one of three ways
| Mode | How the fuel arrives | Typical use |
|---|---|---|
| Ship to ship | A bunker barge or tanker comes alongside | The default in major bunkering ports, and the only option at anchorage |
| Truck to ship | Road tankers at the quayside | Smaller ports, smaller volumes, ports without bunkering infrastructure |
| Shore to ship | Fixed pipeline from a terminal | Dedicated berths, and most LNG bunkering installations |
The mode changes the logistics and the safety envelope. It does not change the documentation: the same record has to be produced whichever way the fuel arrives. The rest of the compliance guides are indexed here.
What actually happens during a bunkering operation
The physical transfer is the short part. Most of the operation is preparation and measurement.
- Nomination. The operator or a bunker trader agrees grade, quantity, port and delivery window with a supplier
- Pre transfer checklist. Signed by both the ship and the supplier before anything flows. It covers scupper plugs, SOPEP equipment, valve line up, communications and the agreed emergency stop signal
- Initial gauging. Tanks are sounded on both sides so there is an agreed starting point
- Transfer. Flow rate and pressure are monitored continuously, with tank levels checked against the expected rate
- Final gauging. Both sides measure again, and any difference between the delivered figure and the received figure is raised now, not later
- Sampling. Samples are drawn continuously through the transfer, then sealed and signed by both parties
- Documentation. The supplier issues the Bunker Delivery Note, and the ship signs for receipt, under protest if the quantities do not agree
Step 7 is the one that carries legal weight. Regulation 18 of MARPOL Annex VI makes the Bunker Delivery Note mandatory and requires the ship to keep it for three years.
The fuel grades you will see on a delivery note
- HSFO, high sulphur fuel oil, above 0.50% sulphur. Usable only with an approved exhaust gas cleaning system
- VLSFO, very low sulphur fuel oil at or below 0.50%, the dominant grade since the 2020 global sulphur cap
- ULSFO, ultra low sulphur fuel oil at or below 0.10%, for use inside Emission Control Areas
- MGO and MDO, marine gas oil and marine diesel oil, distillates used for manoeuvring, auxiliaries and ECA compliance
- LNG, methanol and biofuel blends, the alternative fuels, still a small share of volume but the fastest growing
The quality specification is ISO 8217:2024, published on 30 May 2024. The seventh edition restructured the standard into four tables, added dedicated grades for VLSFO and ULSFO, and for the first time permits biodiesel blends up to B100 in most grades (IBIA). A delivery note that cites the 2017 edition is quoting a superseded specification.
Four samples leave every bunkering, and only one of them belongs to the regulator
Sampling is where most people underestimate bunkering. Four sealed samples are normally drawn:
| Sample | Held by | Purpose |
|---|---|---|
| MARPOL sample | The ship | Evidence of compliance for port state control, retained at least 12 months |
| Ship’s sample | The ship | The operator’s own reference if a dispute arises |
| Supplier’s sample | The supplier | The supplier’s counter evidence |
| Laboratory sample | Sent for testing | Confirms the fuel meets specification before it is burned |
The MARPOL sample is the one with a statutory clock. It must be representative of the fuel actually delivered, sealed and signed by both parties at the point of delivery, and kept until the fuel is substantially consumed and in any case for no less than twelve months (IMO sampling guidelines).
Where bunkering goes wrong
Quantity. The delivered figure and the measured figure disagree. The best known manipulation is the cappuccino effect, where air is worked into the fuel so the volume reads high and settles later. This is why final gauging happens on both sides and why notes get signed under protest.
Quality. The fuel is off specification, sometimes only discovered when the laboratory sample comes back after the fuel is already in the tank. Catalytic fines and stability problems in blended VLSFO are the recurring causes of machinery damage.
Documentation. The delivery note is incomplete, the conformity declaration is vague, or the record ends up in three systems that never reconcile. This is the least dramatic failure and the most common.
“Oil bunkering” means something different in the Niger Delta
One point of confusion worth clearing up. In Nigeria, oil bunkering refers to the theft of crude oil from pipelines, not to fuelling a ship (Council on Foreign Relations). The term is used that way throughout West African reporting and policy writing.
In the shipping sense used everywhere else, bunkering is a routine commercial supply operation.
Bunkering is now where the compliance record is created
For most of its history bunkering was a procurement question: get the right grade, at the right price, at the right port. The measurement existed to settle the invoice.
That is no longer the whole story. The same figures recorded during those few hours now feed obligations with a price attached.
- MARPOL Annex VI sets the sulphur limit the delivery note has to evidence, and requires annual fuel consumption reporting for ships of 5,000 gross tonnage and above
- FuelEU Maritime derives greenhouse gas intensity from what was bunkered, with a penalty of €2,400 per tonne of VLSFO equivalent
- EU ETS requires allowances against the emissions those fuels produce, rising to 100% of reported emissions from 2026
- Green shipping corridors ask partners with no shared parent company to work from the same fuel figures
A bunkering operation lasts a few hours. The number it produces is read years later by a port state inspector, an EU verifier, a charterer and a corridor partner, each holding a separate copy.
VesselChain records the delivery once, at the point of delivery, signed by the accredited verifier the regulation already requires, so every party that depends on the figure is reading the same record rather than reconciling four versions of it. The delivery note stays exactly what MARPOL says it is.
Frequently asked questions
What is bunkering?
Bunkering is the supply of fuel to a ship for its own propulsion and machinery, along with the associated measurement, sampling and documentation. The term comes from the coal bunkers of early steamships.
What is bunkering in shipping?
In shipping, bunkering means refuelling a vessel, usually from a bunker barge alongside, from road tankers at the quay, or through a shore pipeline. It includes issuing a Bunker Delivery Note and drawing sealed fuel samples.
What is bunker fuel?
Bunker fuel is any fuel supplied to a ship for its own use. The main grades are HSFO above 0.50% sulphur, VLSFO at or below 0.50%, ULSFO at or below 0.10%, and the distillates MGO and MDO. LNG, methanol and biofuel blends are also bunkered.
What is a bunkering vessel?
A bunkering vessel, usually called a bunker barge or bunker tanker, is a small tanker that carries fuel to ships and delivers it alongside. Ship to ship delivery from a bunker barge is the most common bunkering mode in major ports.
How long does bunkering take?
It depends on the volume, the transfer rate and the mode. The pumping itself is often a few hours, but the full operation includes the pre transfer checklist, gauging on both sides before and after, sampling and documentation.
What is bunker trading?
Bunker trading is the buying and selling of marine fuel between suppliers and shipowners or operators. A bunker trader arranges grade, quantity, price and delivery window, and is generally distinct from the physical supplier that delivers the fuel.
Which fuel standard applies to bunkers?
ISO 8217 is the marine fuel specification. The current edition, ISO 8217:2024, was published on 30 May 2024, restructured the standard into four tables, added VLSFO and ULSFO grades, and permits biodiesel blends up to B100 in most grades.
Why is oil bunkering associated with theft in Nigeria?
In Nigeria and West African reporting, oil bunkering refers to the theft of crude oil from pipelines rather than to fuelling a ship. It is a separate meaning of the same word and is unrelated to the shipping practice.
