What is a bunker stem? The bunkering process explained

A bunker stem is the confirmed order for a specific fuel to be delivered to a specific vessel at a specific port and time. This guide walks through each stage, from first enquiry to final invoice, and who is responsible for what.

What a stem actually is

In bunkering, to stem a vessel means to secure a confirmed supply of fuel for it. The stem is the agreed order: the vessel, the port, the delivery window, the grade and specification, the quantity range, the price and the payment terms. Once both sides have confirmed it, the supplier plans its barge or truck and the ship plans its tanks around it.

A single delivery often involves more than one grade. Many buyers and service providers count each grade delivered to each vessel as its own stem, because each grade has its own quantity, price, sample set and line on the delivery documents. A vessel taking VLSFO and MGO at the same call therefore has two stems.

Who is involved

• The buyer: usually the owner or manager, or the time charterer when the charter party makes fuel the charterer's responsibility.
• The physical supplier: the company that owns or controls the fuel and delivers it, normally by barge, truck or shore pipeline.
• Traders and brokers: intermediaries who may sit between buyer and physical supplier.
• The vessel: the master and chief engineer, who prepare tanks, witness measurement and sampling and sign the delivery documents.
• The port agent: arranges berth or anchorage details and local permissions.
• The bunker surveyor and laboratory: independent parties who verify quantity and test quality, where appointed.

From enquiry to invoice, step by step

1. Requirement. The vessel and operations team work out what is needed from remaining on board figures, planned consumption, the next legs and any emission control areas on the route.
2. Enquiry. The buyer sends suppliers the vessel name and IMO number, port, ETA and delivery window, grades with the ISO 8217 edition required, minimum and maximum quantities, preferred delivery method and payment terms.
3. Offer. Suppliers reply with a price per tonne and their conditions: barging or delivery charges, surcharges, validity of the offer, payment days and the terms and conditions that will apply.
4. Nomination. The buyer accepts an offer and nominates the vessel to that supplier. This is the point at which the commercial agreement is made.
5. Stem confirmation. The supplier issues a written confirmation setting out the agreed details. Under the BIMCO Bunker Terms 2018, for example, the contract is formed by the general terms together with a confirmation note. Check every line against the nomination before arrival.
6. Pre-delivery. The agent, supplier and vessel exchange final arrival times. The ship prepares empty or near-empty tanks for the new fuel, agrees the sampling method and point, and completes the safety checklist with the barge.
7. Delivery. Tanks are measured before and after, a continuous drip sample is drawn at the receiving ship's manifold throughout the transfer, and the quantity is established by soundings or, where required, a mass flow meter.
8. Bunker delivery note. The supplier issues the BDN, which the chief engineer signs. The samples are sealed, labelled and their seal numbers recorded.
9. Invoice and payment. The supplier invoices against the BDN quantity and the agreed price. Payment falls due on the agreed terms, which in the BIMCO Bunker Terms 2018 default to 30 days unless the confirmation note states otherwise.

The bunker delivery note

The BDN is a statutory document under MARPOL Annex VI regulation 18, not just a commercial receipt. It must contain the information listed in Appendix V of the Annex, including the sulphur content of the fuel. Ships required to hold an IAPP certificate must keep BDNs on board for at least three years after delivery and make them readily available to inspectors.

Two recent changes are worth checking on every delivery. Since 1 May 2024, amendments to Appendix V of MARPOL Annex VI require the BDN to state the flashpoint value where it is below 70°C, or a statement that it was measured at or above 70°C. Since 1 January 2026, amended SOLAS regulation II-2/4.2.1 requires the ship to receive, before bunkering, a declaration signed and certified by the supplier's representative that the fuel meets the SOLAS flashpoint requirement. If either is missing, raise it with the supplier and record it in writing.

If the vessel disagrees with the quantity or any other figure on the BDN, the chief engineer should not simply sign it. Record the concern, issue a letter of protest and inform the office at once.

How much time to allow

There is no fixed timetable. Allow time for suppliers to quote, for the buyer to compare offers properly, and for credit approval if the supplier has not dealt with the buyer before. At major hubs a supplier can often accommodate a stem at short notice; at smaller ports, barges, trucks and specific grades may be limited and need to be booked well ahead.

Late enquiries usually cost money: a supplier quoting for a stem the next morning has little room to plan its barge schedule and will price in that risk. Fixing the requirement as soon as the port and ETA are reasonably firm usually brings more offers and more room to negotiate.

What to check in a stem confirmation

• Vessel name and IMO number, port and delivery location (berth or anchorage).
• Delivery window and how delays on either side will be handled.
• Grade, sulphur limit and the exact specification, including the ISO 8217 edition.
• Quantity range and whether it is stated in metric tonnes.
• Price, currency, and every additional charge such as barging, overtime or small-quantity surcharges.
• Payment terms and the entity that will be invoiced.
• The terms and conditions that apply, including time limits for raising quantity and quality concerns.
• The sampling method and sampling point.

Errors such as the wrong specification edition or a missing surcharge are easy to fix before delivery and difficult to fix afterwards.

How Atlas Bunkering fits in

Atlas Bunkering acts on the owner's side of this process as a handling service, not a supplier or trader. It prepares enquiries, compares offers from trusted suppliers and manages nomination and confirmation on the owner's behalf, without taking ownership of the fuel. The supplier invoices the owner directly at the rate secured. Atlas also recommends an independent bunker surveyor and accredited laboratory testing for every stem, and can arrange both on request.

Questions and answers

Sources

1. IMO: Fuel oil availability and quality, MARPOL Annex VI regulation 18
2. BIMCO Bunker Terms 2018
3. Lloyd's Register Class News 06/24: flashpoint and bunker delivery notes
4. IMO Guidelines for the sampling of fuel oil, resolution MEPC.182(59) (AMSA copy)

This guide is general information, not legal or technical advice. Check the current rules and your engine maker's guidance for your vessel.