Bunker fuel is one of a vessel's largest operating costs, and one of the easiest things to dispute — a few percentage points of quantity discrepancy or an off-spec quality result can mean tens of thousands of dollars, and neither party's word alone settles it. A bunker survey exists to replace that argument with a measured, defensible number.
What You'll Learn in This Lesson
- What a bunker survey actually verifies, and why both quantity and quality matter
- The sampling and measurement workflow that makes a bunker survey defensible
- The core documentation trail behind every bunker delivery
- The most common bunker discrepancies, and what usually causes them
- How to identify the likely cause of a real bunker dispute scenario
Bunker Survey Scope
A bunker survey independently verifies two separate things at the point of fuel delivery or transfer: how much fuel was actually delivered, and whether it meets the quality specification the buyer paid for. Both questions matter independently — a delivery can be the correct quantity but off-spec quality, or the right quality but short on quantity, and each failure mode leads to a different kind of dispute and a different kind of evidence trail.
Bunker Quantity vs Bunker Quality
| Dimension | What's Verified | How It's Measured |
|---|---|---|
| Quantity | Whether the delivered volume matches the quantity invoiced | Tank soundings before and after delivery, converted to volume and mass using calibration tables |
| Quality | Whether the fuel meets the contracted specification (density, viscosity, sulphur content, water content) | Representative samples drawn during delivery, tested against ISO 8217 specification limits |
The vessel's own Remaining on Board (ROB) figure before delivery has to be established accurately first — an inaccurate opening ROB will throw off the entire quantity calculation, even if the delivery measurement itself is done perfectly.
Sampling and Measurement Workflow
Continuous drip sampling throughout the delivery — rather than a single sample at the start or end — is what makes the quality result representative of the whole delivery, not just one moment in it. Samples are sealed on board, in front of witnesses from both the vessel and the bunker supplier, specifically so the chain of custody can't be challenged later if a quality dispute arises.
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A step-by-step checklist covering sounding, sampling, and documentation for a defensible bunker survey.
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Bunker Documentation
| Document | What It Proves |
|---|---|
| Bunker Delivery Note (BDN) | The supplier's record of grade, quantity, and quality delivered — the primary reference for any dispute |
| Sounding Log | The vessel's own before/after tank measurements, independent of the supplier's figures |
| Sample Seal Record | Chain of custody for the fuel samples, from delivery through to lab testing |
| Laboratory Test Certificate | Independent confirmation of whether the fuel met contracted specification |
Whenever the Bunker Delivery Note and the vessel's own sounding log disagree, that gap is usually where a genuine quantity dispute starts — which is exactly why the vessel keeping its own independent sounding record matters, rather than relying solely on the supplier's figures.
Common Bunker Discrepancies
Cat fines (catalytic fines from refining) deserve particular attention — even a delivery that looks quantity-correct and passes a basic quality check can carry cat fines above the safe operating limit, which causes serious engine damage well after the bunker survey is complete and the ship has sailed.
Case Study: A Disputed Short Delivery
Scenario: The Bunker Delivery Note states 500 MT delivered. The vessel's own sounding calculation shows 480 MT received — a 4% shortfall. The supplier insists their meter readings are accurate and the vessel's soundings must be wrong.
Exercise: Identify the Likely Cause
Match each finding to its most likely cause.
1. Lab testing shows water content well above the specification limit.
2. The vessel's sounding calculation shows less fuel received than the Bunker Delivery Note states.
3. Engine damage occurs weeks after bunkering, traced back to abrasive particles in the fuel.
4. The opening ROB figure used in the calculation turns out to have been recorded incorrectly before delivery began.
Best Practices
- Opening ROB independently verified before delivery begins, not taken from memory or estimate
- Continuous drip sampling used throughout delivery, not a single-point sample
- Samples sealed in front of witnesses from both vessel and supplier
- Vessel's own sounding log maintained independently of the supplier's figures
- Cat fines and water content checked specifically, not assumed covered by a general quality pass
- Any discrepancy investigated against both parties' figures before attributing fault
Facing a Bunker Dispute Right Now?
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Frequently Asked Questions
What does a bunker survey verify?
Both quantity (how much fuel was actually delivered) and quality (whether it meets the contracted specification), independently of the supplier's own figures.
Why is continuous drip sampling important?
It makes the quality sample representative of the entire delivery, rather than just one moment, which is essential if the result is later challenged.
What is ROB, and why does it matter for a bunker survey?
ROB (Remaining on Board) is the fuel quantity already on the vessel before delivery. An inaccurate opening ROB throws off the entire quantity calculation, even with a perfect delivery measurement.
What are cat fines, and why are they dangerous?
Catalytic fines are abrasive particles from the refining process. Even fuel that passes a basic quality check can carry cat fines above the safe limit, causing engine damage well after bunkering.
What happens if a bunker delivery is disputed?
Both parties' figures — the supplier's Bunker Delivery Note and the vessel's own sounding log — are compared against the same reference conditions to establish where the discrepancy actually originated.
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