Anatomy of a Bunker Stem: What Actually Happens Between the Enquiry and the Delivery Note

Buying fuel looks, from a distance, like buying anything else. You ask for a price, you accept one, the product arrives, you pay. In practice, a bunker stem is a sequence of six or seven distinct stages, each generating its own document, and the buyer's leverage in any subsequent dispute is determined almost entirely by what was done, or not done, at the right stage. The uncomfortable truth of most bunker claims is that they were lost before anyone knew there was a problem. This can happen at the moment a chief engineer signed a delivery note without a remark, or at the moment a buyer accepted an offer without checking which edition of a fuel standard it referenced.

This is a walk through the stages, what each one is for, and where the exposure sits.

Stage One: The Enquiry

The enquiry is where the buyer sets the terms of the comparison, and a vague enquiry produces offers that cannot be meaningfully compared against each other.

A complete enquiry specifies the vessel name and IMO number, the port and the intended berth or anchorage, the delivery window with a date range rather than a single date, the grade or grades required, the quantity in metric tonnes with any tolerance the buyer will accept, the ISO 8217 edition and table the fuel must meet, the delivery mode expected, and the payment terms sought. Anything left unstated will be filled in by the supplier in their own favor, and the buyer will discover it on the invoice.

The fuel standard reference deserves particular attention because it is the item most often left loose. ISO 8217:2024 is the seventh edition of the marine fuel specification, published on 30 May 2024, and it cancels and replaces the 2017 sixth edition. Where earlier editions used a two-table format for distillates and residuals, the 2024 edition splits fuel types across four tables: distillate and bio-distillate fuels, residual fuel at or below 0.50% sulphur, bio-residual blends, and residual fuel above 0.50% sulphur.

Fuel is still routinely sold against 2010, 2012 and 2017 editions, and the parameters differ. The practical guidance from the P&I clubs is unambiguous. Charter parties and bunker contracts should state the version of the fuel standard, the grade, and any modification to the reference standard, precisely to reduce the scope for disputes. An enquiry that says only "ISO 8217" has already introduced ambiguity into the contract.

Stage Two: The Offer

Offers arrive quickly and expire quickly, and the price is the least interesting part of them. What matters underneath the number is whether the price is net to the buyer or inclusive of intermediary commission, the barge or terminal actually performing delivery, whether that supplier is a physical supplier with its own barges or a trader subcontracting the physical delivery to someone else, the delivery rate, the demurrage and pumping-time terms, the quantity tolerance, the payment terms and the credit basis, and most critically, whose standard terms and conditions govern the sale.

That last point is the one buyers skip and later regret. The supplier's general terms will typically contain the governing law, the arbitration or jurisdiction clause, a lien clause asserting a maritime lien over the vessel for unpaid bunkers, and the time bars for lodging quantity and quality claims. Those time bars are frequently short, sometimes running from the date of delivery rather than from the date a problem was discovered. A buyer who has never read the terms of the supplier they use most often is carrying an unexamined risk.

Stage Three: Stem Confirmation

The stem confirmation is the moment the contract forms. Once the buyer confirms, the supplier has committed product, and withdrawing generally triggers a cancellation charge.

Two things are worth being deliberate about here. The confirmation should restate the agreed terms in full rather than simply accepting by reference, because the written confirmation is the document that will be produced if there is later a dispute about what was actually agreed. And the buyer should know, at this point, whether they are contracting with the physical supplier or with a trader who will subcontract. Those are different counterparties with different balance sheets and different consequences if the chain breaks.

Stage Four: Nomination and Pre-Delivery

The vessel is nominated to the supplier and the barge is scheduled. This is the stage where the operational and the commercial start to converge, and where the buyer's instructions to the vessel matter.

Before delivery begins, the vessel should have taken and recorded soundings of all bunker tanks, and the chief engineer should have the confirmed stem details, grade, quantity, specification, so that what arrives can be checked against what was ordered. If an independent bunker surveyor is being appointed, that appointment happens now, not after a discrepancy appears.

Stage Five: The Delivery

This is where quantity disputes are made and lost.

Fuel is sold by mass and historically delivered by volume, which creates the space in which the industry's most persistent fraud operates. The "cappuccino effect" is the deliberate or inadvertent introduction of air into the fuel stream, through compressed air, an open valve to an empty tank, or turbulence at high loading rates. A volumetric meter registers the aerated fuel as volume, and the tank soundings appear correct while the air remains in suspension. When the air settles out, the level drops and the shortfall appears. A related manipulation involves the barge citing customs seals or a seized sounding cock as grounds for refusing tank gauging, leaving the vessel with meter figures as the only available measurement.

Mass flow metering addresses the physics of the problem but does not eliminate the dispute. In Singapore, the BDN figure presented to the vessel has been the mass flow meter figure since 1 January 2017, and bunker barges neither accept sounding-derived figures nor participate in the sounding process. That does not mean the vessel should stop sounding. Soundings before and after delivery remain the vessel's only independent record, and where they differ from the BDN, a letter of protest should be issued. Suppliers will usually decline to accept or sign it, but it stands as evidence of the discrepancy, and charterers should be informed immediately.

Where aeration is suspected during delivery, the response is operational rather than commercial. The bunkering should be stopped, the source of the air identified, and a letter of protest presented to the barge master. Samples from affected tanks can be examined in a clean glass container for bubbles, and the density checked against the figure declared on the delivery note. A density lower than declared, allowing for temperature, alongside visible bubbles, is indicative. Where the results are unsatisfactory, the protest should state the reason specifically, an entry should be made in the engine logbook, and tank soundings should be double-checked roughly half a day after delivery once any entrained air has had time to settle.

Stage Six: Sampling

Two categories of sample come off a delivery and they are not interchangeable.

The MARPOL sample is a regulatory document. It must be drawn continuously throughout the bunkering period using a manual valve-setting continuous drip sampler or an automatic sampler, with the sampling equipment and receiving container sealed throughout the delivery, and it must be at least 400 ml. It is retained under the ship's control until the fuel is substantially consumed and in any event for not less than 12 months from delivery. Its purpose is compliance verification by a port state, and it is not to be used for commercial disputes. It is handed over to authorities, not to a testing lab acting for the buyer.

The commercial samples are the ones that matter for a quality claim. These are drawn at the same time, sealed in the presence of both the barge and vessel representatives, and labelled with vessel name, IMO number, date, port and grade. An unsealed or unlabeled sample will generally be inadmissible in P&I proceedings. It is recommended practice, and a requirement under Singapore's SS 600 standard, that all seal numbers relating to samples drawn be recorded on the delivery note itself, so that the sample and the document are cross-referenced.

Stage Seven: The Bunker Delivery Note

The BDN is where the regulatory and commercial functions of the stem collide, and buyers routinely underestimate it on both counts.

As a regulatory instrument, it is mandated by MARPOL Annex VI regulation 18.5, must contain at minimum the information set out in Appendix V to the Annex, must be kept readily available on board for inspection, and must be retained for three years after delivery. The IMO confirmed at MEPC 80 that electronic BDNs are acceptable, provided they are protected against edits and revisions and carry a verification method enabling authentication. The three-year retention requirement applies identically.

As a commercial instrument, it is the supplier's declaration of what was delivered, and this is the part that decides claims. A quantity stated on the BDN and not challenged at the time of delivery, by written protest or notation on the document itself, is treated as accepted by the receiving vessel. Where the vessel's figures show a material shortfall after re-sounding with all parties present, the guidance from the clubs is direct. Do not sign the receipt as presented. In circumstances of genuine doubt, the correct step is to withhold signature, contact owners, charterers and the local club correspondent, and determine the course of action before the barge departs.

Signing clean is not a courtesy. It is a concession, and it is usually irreversible.

After Delivery

Commercial samples go for testing. Results typically return within a few days, and if the fuel is off-specification the clock on the supplier's contractual time bar is already running, which is why the terms reviewed at Stage Two matter now rather than then. Off-spec fuel raises its own set of questions about whether it can be treated onboard, segregated, debunkered, or used at all, and those are engineering decisions with commercial consequences that should be made with the club involved.

The rest is straightforward. The delivery is reconciled against the invoice, the BDN is filed for its three-year retention, and the MARPOL sample is logged and stored for its twelve months.

What This Means for Buyers

Most of the leverage in a bunker transaction sits at two points, and neither of them is the price negotiation.

The first is the enquiry and the offer terms, specifying the ISO edition and table, knowing which supplier is physically delivering, and having read the general terms that govern the sale including the time bars. That work happens before any fuel moves and costs nothing but attention.

The second is the delivery itself, soundings taken and recorded independently of the barge's figures, samples drawn continuously and sealed jointly with the seal numbers recorded on the BDN, and a willingness to withhold signature or annotate the delivery note when the numbers do not agree. A master or chief engineer who has been told by the office that a clean signature is expected regardless has been placed in an impossible position, and the buyer has given away their claim in advance.

Everything between those two points is logistics. The two points themselves are where the money is.