MARPOL Annex VI Reg 18: bunker delivery note

Background: MEPC.176(58) 2008 amendments + Reg 18 introduction

The original 1997 text of MARPOL Annex VI, adopted at the International Conference of the Parties to MARPOL convened in London in September 1997, established a fuel-quality and documentation regime in Regulation 18 (Chapter 3 of the original Annex VI). The 1997 text required suppliers to provide a Bunker Delivery Note recording basic fuel characteristics and required ships to retain a representative sample. The 1997 BDN was a relatively short document and the sample-handling chain of custody was lightly specified, since the principal use of the data at that time was the 3.5% to 4.5% global cap with the original SECA limits of 1.5% and 1.0%, both of which could be verified by relatively coarse measurement.

By the late 2000s, the air-pollution chapter of Annex VI was being comprehensively revised in light of the science of secondary sulphate aerosol, the increased ambition of the 0.50% global cap by 2020 (or 2025), the introduction of the North American ECA, and the introduction of the Tier I, II and III NOx regime under the rewritten Regulation 13. Regulation 18 also needed substantial strengthening: the BDN had to record sulphur content with sufficient precision to verify a 0.50% or a 0.10% cap, the sample had to be retained long enough for PSC and flag-state laboratory testing (typically 30-60 days from delivery to PSC sampling, plus 60-90 days for laboratory turnaround), and the chain of custody had to be tight enough that a non-compliant operator could not credibly dispute the sealed-sample test result.

The 2008 amendments to Annex VI were adopted by Resolution MEPC.176(58) on 10 October 2008, with entry into force on 1 July 2010. The 2008 amendments completely rewrote Regulation 18, adding Appendix V to Annex VI (the BDN minimum-content schedule), introducing the explicit 3-year on-board retention requirement for the BDN (Reg 18.6), the 12-month retention requirement for the representative sample (Reg 18.8.1), the 1-litre minimum sample volume, and the requirement that the sample be labelled and sealed by the supplier in the presence of the chief engineer or a representative of the receiving ship. The 2008 amendments also introduced the requirement that the supplier register the BDN with the port state authority (typically the bunkering-port flag administration), establishing the supplier-side audit trail that complements the on-board document.

The 2008 amendments left two important gaps. First, the physical location at which the sample was to be drawn was not specified beyond a generic requirement that the sample be representative of the delivered fuel; in practice, suppliers were drawing samples from a tap upstream of the receiving ship’s manifold, where the supplier could in principle substitute a clean sample for the actually delivered fuel. Second, the sealing protocol specified that the sample be sealed but did not specify how the seal was to be applied, by whom, or how the chain of custody was to be documented from the manifold to the on-board sample locker.

Resolution MEPC.250(66), adopted on 4 April 2014 with entry into force on 1 January 2016, addressed both gaps. The 2014 amendments specified that the spot sample be drawn at the receiving ship’s manifold, by continuous sampling during the entire bunker delivery, using a sampling apparatus (typically a stainless-steel drip-sampler) connected at the manifold flange. The 2014 amendments further specified that the sample be sealed by the supplier in the presence of the chief engineer or a designated representative of the receiving ship and that the chain-of-custody label record the ship’s name, the IMO number, the bunker port, the delivery date, the BDN reference number, and the signatures of both parties. These requirements are the structural backbone of the modern Reg 18 sample regime and are the basis on which PSC sample test results are admissible against operator disputes.

A further refinement arrived with Resolution MEPC.305(73), adopted on 26 October 2018 at MEPC 73. The 2018 amendments served three purposes. First, they added new Regulation 14 sampling-point requirements: Reg 14.8 now designates approved fuel-oil sampling points on board (the in-use sample point in the fuel-supply line to the engine and the onboard sample point at the storage tank), separate from the Reg 18.8.1 delivered sample point at the manifold. Second, MEPC.305(73) added Appendix VI to Annex VI, the formal verification procedure for fuel-oil samples (discussed below). Third, the 2018 amendments tightened the BDN consistency requirement: a deviation greater than 0.05% absolute between the BDN-declared sulphur and the test-sample sulphur is treated as prima facie non-compliance by the supplier (subject to a flag-state appeal). The 2018 amendments also clarified that ships carrying high-sulphur fuel without a scrubber for non-fuel purposes (research, calibration) must so record on the BDN.

Reg 18 structure: BDN + sample + supplier registration

Regulation 18 has three operational pillars that together form the verification chain:

• The BDN is the paper or electronic document issued by the supplier and signed by both the supplier and the chief engineer. It records the fuel characteristics and is retained on board for 3 years and at the supplier’s office for at least 3 years. The BDN is the document that PSC officers inspect first.
• The representative sample is the physical sealed bottle of the actually delivered fuel, drawn at the manifold and retained on board for 12 months. The sample is the physical evidence that backs up (or contradicts) the BDN declaration.
• The supplier registration is the obligation of the supplier to register the BDN with the port state authority of the bunkering port, typically the flag administration of the port. The registration creates the supplier-side audit trail and is the basis on which a flag administration can verify that suppliers are not issuing BDNs for fuel that does not exist.

The three pillars together support a two-way verification: the BDN is checked against the on-board sample (manifold-sample sulphur should match BDN-declared sulphur), and the BDN is checked against the supplier registration (the BDN reference number on board should match the supplier registration record). A discrepancy at either junction is a Reg 18 deficiency.

BDN content requirements: Appendix V, 15 fields

The BDN must record the 15 fields specified in Appendix V of Annex VI (added by MEPC.176(58)). The fields are:

1. Name of receiving ship as recorded on the IAPP supplement.
2. IMO number of receiving ship, the seven-digit identifier assigned by the IMO Ship Identification Number Scheme.
3. Port of bunker delivery, identified by name and country.
4. Date of commencement of delivery, in dd-mm-yyyy format. Where the delivery spans multiple days, the start and end dates are both recorded.
5. Name and address of the supplier, as registered with the bunkering-port authority.
6. Product name, as a commercial description (e.g. “VLSFO 0.50% RMG-380”, “MGO DMA”, “ULSFO 0.10% RMD-80”).
7. Quantity (metric tonnes), the mass actually delivered as determined by the supplier’s mass-flow meter or by the 6-tank gauge method on the supplier barge with corrections for density and temperature.
8. Density at 15 degrees C (kg/m³), determined by ISO 3675 (laboratory) or ISO 12185 (oscillating U-tube), used for the volume-to-mass conversion in the supplier’s flow-meter or gauge calculation.
9. Sulphur content (% m/m), determined by ISO 8754 (XRF) or ISO 14596 (WDXRF) at the supplier’s laboratory. Reported to two decimal places.
10. Declaration by the supplier, in prescribed wording: “I, the undersigned, declare that the fuel oil delivered is in conformity with paragraph 1 (or 4) of Regulation 14 and Regulation 18 of Annex VI of MARPOL.” For ECA-supplied fuel, paragraph 4 (the 0.10% limit) applies; for global-cap fuel, paragraph 1 (the 0.50% limit) applies.
11. Flash point (degrees C), determined by ISO 2719 (Pensky-Martens closed cup). Must be at least 60 degrees C for fuel intended for main propulsion per SOLAS Reg II-2/4.2.
12. Other parameters as agreed, typically including viscosity at 50 degrees C (cSt), water content, ash content, and pour point. ISO 8217 specification grades are commonly cited here.
13. Signature and stamp of the supplier representative.
14. Signature and stamp of the chief engineer or designated representative of the receiving ship.
15. BDN reference number, a unique identifier assigned by the supplier and used to cross-reference the supplier registration record and the on-board sample seal.

The fields above are the minimum under MARPOL. National jurisdictions and charter-party clauses commonly add fields such as the supplier IMO number (where the supplier barge has one), the time of commencement and completion, the temperature of delivery, the VPP correction (for vapour pressure), and the micro carbon residue (CCAI/CII fuel-quality indicators).

Fields 8 (density) and 9 (sulphur) are the two parameters most likely to be tested at PSC inspection, since they govern respectively the volume-to-mass conversion (basis of the commercial dispute under the BIMCO Bunker Clauses) and the regulatory compliance under Reg 14.

BDN field reference table

BDN retention: 3 years on board

Regulation 18.6 of Annex VI requires the BDN to be retained on board for a period of at least 3 years from the date of delivery. The 3-year period covers two PSC inspection cycles plus the 5-year IAPP renewal survey horizon, ensuring that PSC officers and class society surveyors can review the bunker history of the previous 1-2 years at any inspection.

The BDN is retained as a paper document in the original signed form, or as an electronic copy where the flag administration accepts electronic record-keeping. The on-board file is typically kept in the engine control room (ECR) or in the chief engineer’s office, organised chronologically by delivery date with a cross-reference index by BDN reference number. A loose-leaf binder is the most common physical format; some operators use PDF storage on the ship-management system.

The 3-year retention period is the minimum under MARPOL. Many flag administrations require longer retention (5-7 years) for tax and insurance reasons, and most P&I clubs recommend that the BDN be retained for the entire life of the ship as part of the bunker history file, since the BDN is the primary evidence in any future bunker-quality dispute. The marginal cost of retaining a BDN beyond 3 years is negligible (a single page or PDF), so the 3-year minimum is rarely the binding constraint.

The supplier-side retention is parallel: the supplier must retain the BDN at its office for at least 3 years under the supplier-registration requirement of Reg 18.9. This enables flag-state audits of the supplier’s books, cross-checking the supplier’s claimed deliveries against the actual fuel handled.

MARPOL fuel oil sample: Reg 18.8.1, 12-month retention

Regulation 18.8.1 of Annex VI requires that, at the time of bunker delivery, a representative sample of the delivered fuel oil be drawn, labelled and sealed, and retained on board for a period of not less than 12 months from the date of delivery, or until the fuel oil is substantially consumed, whichever is later. The minimum sample volume is 1 litre, drawn into a container suitable for laboratory analysis (typically an aluminium or HDPE bottle).

The 12-month retention period is calibrated to the PSC plus flag-state laboratory turnaround: a PSC inspection that occurs 6-9 months after a particular bunker delivery still has a valid sample to test, and the 60-90 day flag-state laboratory turnaround can be completed within the 12-month window. After 12 months (and after the fuel has been substantially consumed), the sample may be discarded, but most operators retain samples for 24 months as a precautionary measure, since some flag administrations have requested historical samples in retrospective enforcement actions.

The on-board sample storage is typically a dedicated locker in the engine room, with adequate ventilation and protection from heat and direct sunlight. Sample bottles are stored upright, with the seal intact, organised chronologically by delivery date with a cross-reference to the BDN reference number on the seal label. The sample locker is itself sealed at PSC entry and is opened only by the PSC officer in the presence of the chief engineer.

The sample is drawn at the manifold during the bunker delivery using a continuous-flow drip sampler that collects a small volume continuously throughout the delivery. The continuous-flow method ensures that the sample is representative of the entire delivery rather than the first or last fraction, which is important because some suppliers pump a cleaner fuel “heel” at the start or end of a delivery.

Sample types and retention summary

Sealing + chain-of-custody requirements (MEPC.250(66) 2014 amendments)

The 2014 amendments under Resolution MEPC.250(66) specified the sealing and chain-of-custody requirements with substantially greater precision than the 2008 baseline. The current requirements are:

• The sample bottle must be sealed at the time of drawing by the supplier, in the presence of the chief engineer or designated representative of the receiving ship.
• The seal must be a tamper-evident, uniquely numbered seal (typically a plastic security seal with a serial number) that cannot be removed or replaced without visible damage.
• The seal label must record the ship’s name, the IMO number, the bunker port, the delivery date, the BDN reference number, the seal serial number, and the signatures of the supplier representative and the chief engineer.
• The seal must be affixed to the sample bottle in such a way that the sample cannot be accessed without breaking the seal.
• The chain-of-custody record (a written log) must record the transfer from the manifold to the on-board sample locker, the identity of the person performing the transfer, and the date and time of the transfer.

A sample with a broken seal, a mismatched seal serial number (between the seal label and the chain-of-custody log), or an incomplete chain-of-custody record is inadmissible as evidence in a PSC sulphur-compliance dispute. The PSC officer is required to record the chain-of-custody status as part of the inspection report; a non-compliant sample is treated as if the sample did not exist, and the PSC may then draw a fresh sample from the bunker tank for laboratory analysis. A fresh in-tank sample is, however, less probative than a manifold sample, since the in-tank fuel has been mixed with previously bunkered fuel.

The chain-of-custody requirement is the legal anchor of the Reg 18 enforcement regime. Without the chain-of-custody, the sealed-sample test result is reduced to a contestable laboratory finding rather than a presumed-correct regulatory measurement.

Sample-port location requirements and the three distinct sample points

The 2014 amendments specified that the Reg 18 spot sample must be drawn at the receiving ship’s manifold, defined as the flange on the receiving ship’s side at which the supplier hose connects. The sampling port is typically a 3/4-inch or 1-inch stub on the manifold spool piece, fitted with a stainless-steel drip-sampler connected via a quick-release coupling.

The 2018 amendments under MEPC.305(73) then added two further designated sample points under the new Regulation 14.8. This creates three distinct sampling locations in the Reg 14/Reg 18 verification framework:

1. Manifold sample (Reg 18.8.1): the MARPOL delivered sample, drawn during delivery, sealed and retained 12 months. This is the primary enforcement instrument for the delivered fuel.
2. In-use sample (Reg 14.8): drawn from the fuel supply line between the service tank and the main engine (or auxiliary). This captures the fuel actually entering the engine and accounts for any blending or contamination between delivery and combustion.
3. Onboard sample (Reg 14.8): drawn from the service or storage tank. This captures the in-tank fuel at the time of inspection and may reflect a mixture of multiple deliveries.

PSC officers use the in-use and onboard sample points to verify ongoing Reg 14 compliance independent of the delivered-sample record. Where a vessel has mixed compliant and non-compliant fuel in a tank, or where a delivery postdates the last PSC inspection, the in-use sample is the most direct check. The Appendix VI verification procedure applies to all three sample types with the same 0.59R statistical rule (see below).

The drip-sampler for the manifold draws continuously, bleeding a small flow (typically 5-10 ml/minute) from the main bunker line throughout the delivery, into a sample collection vessel (typically a 5-litre stainless-steel can). At the end of the delivery, the collected sample is decanted into the regulatory sample bottle, with the remainder retained as the supplier sample. The continuous-flow method is required because batch sampling (a single discrete draw at the start, middle or end of the delivery) is unrepresentative if the supplier alters the fuel composition during delivery.

The location at the receiving ship’s manifold (rather than at the supplier barge) matters because the manifold sample captures the fuel as actually delivered to the ship, including any contamination or composition change occurring in the supplier hose or the supplier barge’s pumping system. A sample drawn upstream of the supplier hose would miss such effects.

The detailed apparatus design is governed by Resolution MEPC.182(59) of 2009, the 2009 Guidelines for the Sampling of Fuel Oil for Determination of Compliance with the Revised MARPOL Annex VI, which is the reference document for sampling apparatus and sampling procedure.

Appendix VI verification procedure: 0.59R, 0.53% + 0.11% decision thresholds

Appendix VI of Annex VI, titled “Verification Procedure for a MARPOL Delivered Fuel Oil Sample”, was added by Resolution MEPC.305(73) and applies to all Regulation 14 fuel-oil samples (delivered, in-use, and onboard). It is the statistical framework that converts a laboratory test result into a compliance or non-compliance finding.

The core of the procedure is the 0.59R rule. ISO test methods publish a reproducibility value R, which is the maximum acceptable difference between two results obtained by different laboratories using the same method on the same fuel. For ISO 8754 (energy-dispersive XRF sulphur) at the 0.50% sulphur level, the published reproducibility is on the order of 0.04% absolute; 0.59 × 0.04 = 0.024%. The Appendix VI rule states:

A fuel oil sample is considered to meet the applicable limit if the mean measured value does not exceed the limit by more than 0.59R for the applicable test method.

In practice, the decision thresholds derived from this rule are:

• For the 0.50% global cap: effective decision threshold ≈ 0.53% m/m (0.50% + 0.59 × ~0.05% reproducibility at that concentration).
• For the 0.10% ECA cap: effective decision threshold ≈ 0.11% m/m (0.10% + 0.59 × ~0.017% reproducibility at that concentration).

These thresholds reflect measurement uncertainty, not a regulatory relaxation of the limit. A vessel whose sample tests at 0.52% is not automatically compliant; the 0.59R allowance is the statistical criterion that defines how far above 0.50% a result must land before the procedure treats it as a compliance failure at 95% confidence. A result at 0.54% exceeds the 0.53% threshold and is a non-compliance finding under Appendix VI.

The Appendix VI procedure is applied by the flag-state laboratory as follows: the sealed sample is tested in duplicate; the two results are averaged; and the averaged value is compared against the specification limit adjusted by 0.59R. The procedure operates at a 95% confidence level, meaning that a result above the decision threshold would arise from sampling and measurement variability alone fewer than 5% of the time when the fuel is actually on-spec. That confidence level is the legal threshold for imposing a penalty on the operator or the supplier.

The 0.05% BDN-vs-sample tolerance (separate from Appendix VI)

The 0.05% absolute BDN-vs-sample tolerance introduced by MEPC.305(73) is a separate instrument from the Appendix VI verification procedure. Its specific operation is:

When the difference between the BDN-declared sulphur and the tested sample sulphur exceeds 0.05% absolute, the excess triggers prima facie supplier liability: the supplier bears the burden of demonstrating that the discrepancy arose from sampling or test-method error rather than from delivering a fuel whose actual sulphur differed from the declared value. Below 0.05%, the discrepancy sits within the combined measurement and sampling uncertainty of the ISO 8754 method and is not treated as evidence of non-compliance.

ISO 8754 carries a typical reproducibility of about 0.02 to 0.03% absolute at the 0.50% level. A discrepancy under 0.05% is therefore well within combined method uncertainty; a discrepancy above 0.05% falls outside that envelope. The rule is calibrated so that a supplier blending to a nominal 0.45% target (with 0.05% blending tolerance) and delivering at up to 0.50% will not be penalised for BDN-vs-sample differences that arise from legitimate test-method scatter, but a supplier issuing a 0.45% BDN for fuel that actually tests at 0.52% cannot hide behind method uncertainty.

ISO 8217 fuel-specification relationship (parallel but separate)

The ISO 8217 standard, Petroleum products - Fuels (class F) - Specifications of marine fuels, is the industry-standard fuel-quality specification that runs in parallel with the regulatory BDN regime but is legally distinct. Where the BDN is the regulatory document required by MARPOL, ISO 8217 is the commercial specification cited in the supplier-buyer fuel-supply contract.

ISO 8217 specifies fuel grades in two main families:

• Distillate fuels (Annex A), grades DMX, DMA, DMB, DMZ, with viscosity at 40 degrees C in cSt, sulphur in % m/m, and other parameters. DMA is the standard MGO grade.
• Residual fuels (Annex B), grades RMA-10, RMB-30, RMD-80, RME-180, RMG-180, RMG-380, RMG-500, RMG-700, RMK-380, RMK-500, RMK-700, with viscosity at 50 degrees C in cSt, sulphur in % m/m, and other parameters. RMG-380 is the historical workhorse HFO and is now the most common VLSFO grade.

The BDN typically cites the ISO 8217 grade in field 6 (product name) and in field 12 (other parameters). PSC officers and class society surveyors use the ISO 8217 grade as a shorthand for the expected fuel parameters, but the regulatory parameters (sulphur, density, flash point) are those recorded on the BDN itself, not those of the ISO 8217 grade.

The relationship between ISO 8217 and Reg 18 is complementary but not identical:

• ISO 8217 specifies commercial-quality parameters (viscosity, water, ash, vanadium, sodium, aluminium-plus-silicon, total sediment) that are not regulated by MARPOL.
• Reg 18 requires the BDN to record sulphur, density and flash point, which are regulatory parameters; ISO 8217 also specifies these but with slightly different limits (ISO 8217 RMG-380 sulphur limit is the regulatory limit at the time, not necessarily the actual fuel sulphur).
• A fuel on-spec to ISO 8217 is not necessarily compliant with Reg 14: a 3.0% RMG-380 was on-spec to ISO 8217:2010 (with a 3.5% maximum sulphur) but is non-compliant with the 0.50% global cap.
• A fuel compliant with Reg 14 is not necessarily on-spec to ISO 8217: a 0.45% VLSFO with high cat-fines or stability problems may be compliant with Reg 14 but off-spec to ISO 8217 RMG-380.

The two regimes are therefore independent compliance checks: the BDN evidences Reg 14 compliance, the ISO 8217 test report (typically issued by a third-party laboratory such as DNV PS, VPS, Bureau Veritas Marine Fuel, or Lloyd’s Register FOBAS) evidences commercial-quality compliance, and a fuel must pass both to be commercially and regulatorily acceptable.

ISO 8217:2024 update: VLSFO + ULSFO + biofuels Annex F

The ISO 8217 standard was first published in 1987 and has been revised in 1996, 2005, 2010, 2017, and 2024. The ISO 8217:2024 revision, published in May 2024, is the most significant update since the 2010 edition and addresses three structural changes in the marine fuel market:

• The emergence of VLSFO (very-low-sulphur fuel oil) at 0.50% sulphur as the dominant non-ECA bunker grade post-2020. VLSFO is a heterogeneous category, with viscosity ranges from 30 cSt to 380 cSt and density ranges from 880 to 990 kg/m³. The 2024 edition introduces a VLSFO-specific characterisation within the existing residual-grade framework.
• The emergence of ULSFO (ultra-low-sulphur fuel oil) at 0.10% sulphur as the dominant ECA bunker grade. ULSFO is similarly heterogeneous.
• The emergence of bio-based marine fuels, including FAME blends (B7, B24, B30, B100) and HVO (hydrotreated vegetable oil). The 2024 edition adds a new Annex F specifying bio-component-blended fuel grades, with parameters for FAME content, oxidation stability, water content, and acid number.

The Annex F bio-fuel grades are particularly important under FuelEU Maritime and the IMO Net-Zero Framework, since both regulations incentivize the use of bio-fuels via the GHG intensity target. A FuelEU compliance pathway often involves a B30 blend (30% FAME by volume in residual or distillate), which the 2024 ISO 8217 Annex F specifies. The BDN under Reg 18 must record the bio-fuel content (where present), and the parallel FuelEU BDN under Article 9 must record the renewable share and the certified GHG intensity of the bio-fuel.

The 2024 edition also tightens the stability specification (total sediment after thermal aging, TSP) for VLSFO grades, in response to the persistent stability problems observed in 2019-2020 with early VLSFO blends. The test is now applied to aged fuel rather than fresh fuel, which is more representative of the fuel’s behavior after storage and heating on board.

Relationship to SOLAS Reg II-2/4.2 (flash point ≥60°C)

Field 11 of the BDN records the flash point of the delivered fuel, in degrees Celsius, determined by ISO 2719 (Pensky-Martens closed cup). The flash point must be at least 60 degrees C for fuel intended for main propulsion under SOLAS Regulation II-2/4.2.1.1, the International Convention for the Safety of Life at Sea (SOLAS) requirement on flammable liquids.

The 60-degree flash-point limit reflects the fire-safety boundary between flammable and combustible liquids in the IMO maritime classification. A fuel with flash point below 60 degrees C is flammable and requires special handling (inerting, vapour control, restricted handling locations); a fuel with flash point at or above 60 degrees C is combustible and may be handled in standard fuel-oil tanks and piping.

Marine gas oil (MGO) typically has a flash point of 60-70 degrees C (just above the limit), residual fuel oils typically have flash points of 80-120 degrees C (well above the limit), and bio-fuel blends typically have flash points in the same range as the host fuel. Some niche fuels (kerosene, jet-fuel-equivalent grades) have flash points below 60 degrees C and are not permitted for marine main propulsion under SOLAS unless special precautions are taken (typically only in naval vessels or in IGF-Code low-flashpoint-fuel installations).

The 2014 amendments under MEPC.250(66) explicitly require the BDN flash point to be recorded at the time of delivery; a flash point below 60 degrees C is a SOLAS deficiency and is recorded on the IAPP supplement (under the fuel-quality remarks) and in the bunker record. Where a flash point below 60 degrees C is recorded, the fuel may not be transferred to a standard fuel-oil tank without flag-state approval.

The flash point requirement is independent of sulphur content and independent of viscosity. A 0.10% ULSFO with flash point 55 degrees C is a SOLAS deficiency irrespective of its Reg 14 compliance; a 1.0% RMG-380 with flash point 90 degrees C is a Reg 14 deficiency (post-2020) but SOLAS-compliant. PSC inspections are therefore required to check both the flash point (SOLAS) and the sulphur content (MARPOL).

FuelEU Maritime BDN extension (Article 9)

Regulation (EU) 2023/1805, commonly known as FuelEU Maritime, entered into force on 1 January 2025 and applies to all commercial vessels above 5,000 GT calling at EU/EEA ports. Article 9 of FuelEU establishes a parallel BDN regime for fuel-tracking purposes.

The Article 9 BDN must record the same minimum fields as the MARPOL BDN under Reg 18, plus the following additional FuelEU-specific fields:

• Renewable share of the fuel (% by energy), distinguishing between bio-based (FAME, HVO, biomethane) and non-bio-renewable (RFNBO, e-methanol, e-ammonia) fuels.
• Certified GHG intensity of the renewable component, in g CO₂e/MJ, on a well-to-wake (WTW) basis as defined in FuelEU Annex II.
• Sustainability certification reference, citing the voluntary scheme (typically ISCC EU or REDcert EU) under which the bio-fuel is certified.
• Mass and energy of the renewable component separately from the host fuel.

The Article 9 BDN is issued in addition to the MARPOL Reg 18 BDN; the two documents are typically combined into a single physical or electronic record with the FuelEU fields appended to the MARPOL fields. The supplier must register the Article 9 BDN with THETIS-MRV (the EU monitoring system) within 5 working days of the delivery, in addition to the MARPOL supplier-registration obligation.

The Article 9 BDN is the fuel-tracking anchor for the FuelEU GHG intensity calculation. The renewable-share data and the certified GHG-intensity data are used to compute the actual WTW GHG intensity of the year’s fuel mix, which is then compared to the target intensity under FuelEU Article 4. A vessel without Article 9 BDNs for its renewable fuel cannot claim the renewable benefit and is treated as having burnt default-value fossil fuel (with the Annex II default values such as 91.6 g CO₂e/MJ for VLSFO, 90.6 g CO₂e/MJ for HFO, 90.5 g CO₂e/MJ for MGO).

The Article 9 BDN is also the audit trail for the verifier under FuelEU Article 19; the verifier (typically a class society in its verification arm, such as DNV V, LR Quality Assurance or Bureau Veritas) reviews the Article 9 BDNs as part of the annual emissions report verification.

IMO Net-Zero Framework BDN extension (Chapter 4 ter, forthcoming)

The IMO Net-Zero Framework, agreed in principle at MEPC 83 in April 2025 and scheduled for formal adoption in October 2025 with entry into force in 2027, will introduce a third parallel BDN regime for global GHG-fuel-intensity (GFI) tracking. The framework adds a new Chapter 4 ter to MARPOL Annex VI (Reg 30 onwards), establishing the global fuel intensity (GFI) target and the two-tier carbon-pricing structure (base and direct compliance).

The Chapter 4 ter BDN must record the following additional GFI-specific fields, on top of the MARPOL Reg 18 minimum:

• Certified GFI of the fuel in g CO₂e/MJ on a WTW basis, as defined in the GFS methodology (the IMO equivalent of FuelEU Annex II).
• Renewable / non-renewable breakdown of the fuel, similar to FuelEU.
• Sustainability certification under an IMO-recognised scheme (the IMO is expected to recognise ISCC EU, REDcert EU and a forthcoming IMO-specific scheme).
• Reference to the FuelEU Article 9 BDN, where the same fuel is also covered by FuelEU.

The Chapter 4 ter BDN is intended to be harmonised with the FuelEU Article 9 BDN, so that a single supplier-issued document can serve both regimes. Industry consultation under the IBIA and BIMCO has urged the IMO to adopt the EU template directly, to avoid the supplier-side burden of two parallel registration systems.

The Chapter 4 ter BDN is the fuel-tracking anchor for the IMO GFS calculation. The certified GFI data is used to compute the actual WTW GHG intensity of the year’s fuel mix, which is then compared to the GFI target for the year (the target follows a glide-path from 89.6 g CO₂e/MJ in 2027 to approximately 17 g CO₂e/MJ by 2050, per the MEPC 83 outcome). A vessel without Chapter 4 ter BDNs for its renewable fuel cannot claim the renewable benefit and is treated as having burnt default-value fossil fuel, with the corresponding GFI penalty payable under the carbon-pricing structure.

The relationship between Reg 18 (the original BDN), FuelEU Article 9 (EU regional BDN extension) and the forthcoming Chapter 4 ter (global IMO BDN extension) is nested: every commercial vessel will be required to issue and retain a Reg 18 BDN; vessels calling at EU/EEA ports add the Article 9 fields; from 2027, all vessels add the Chapter 4 ter fields. The supplier-side burden is therefore expected to consolidate into a single combined BDN template with Reg 18 as the base layer and the regional / global extensions as add-ons.

Class society implementation: BDN review at IAPP renewal survey

The BDN and sample regime is verified by the classification society (acting as a recognised organisation on behalf of the flag administration) at the periodic IAPP renewal survey, which occurs at the 5-year IAPP cycle with intermediate annual surveys.

At the annual IAPP survey, the surveyor reviews:

• The on-board BDN file for the previous 12 months. The surveyor checks that a BDN exists for every recorded bunker delivery (cross-referenced against the Oil Record Book and the bunker tank logs).
• The BDN content of a sample of recent BDNs (typically 5-10), checking that all 15 fields are completed and the sulphur declaration is consistent with the applicable cap.
• The on-board sample locker, checking that samples exist for every recorded bunker delivery within the previous 12 months, that the seals are intact, and that the chain-of-custody labels are complete.
• The bunker tank log and the Oil Record Book Part I entries for each delivery, cross-referenced against the BDN.

At the 5-year IAPP renewal survey, the surveyor performs the same review but with a longer look-back (typically the previous 5 years for the BDN file, the previous 12 months for the sample locker). The renewal survey also reviews the fuel-changeover procedure and the IAPP supplement entries for ECA transits.

A deficient BDN file (missing BDNs, incomplete fields, inconsistent sulphur declarations) results in a survey condition (a corrective action with a deadline) or, in serious cases, a withholding of the IAPP renewal, which prevents the vessel from trading until the deficiency is corrected. A deficient sample locker (missing samples, broken seals, incomplete chain-of-custody) is treated similarly.

The class society retains the BDN review records as part of its survey file, which is auditable by the flag administration and by the IACS as part of the recognised-organisation audit programme. The records are typically retained for at least 10 years after the survey.

PSC inspection focus: BDN vs IAPP vs sample test

Port state control (PSC) inspection of BDN compliance is governed by the Tokyo MoU, the Paris MoU, the USCG Port State Control Programme, and the various other regional MoUs (Indian Ocean MoU, Caribbean MoU, Mediterranean MoU). The inspection sequence at a typical PSC visit is:

1. Document review: The PSC officer reviews the IAPP supplement, the BDN file, and the Oil Record Book. The IAPP supplement records the fuel-changeover dates and the ECA transit log, which must be consistent with the BDN-recorded fuel grades.
2. BDN-IAPP cross-check: The officer verifies that the IAPP-recorded fuel grade for each ECA transit is consistent with the BDN-declared sulphur content of the fuel actually in the day tank during that transit.
3. Sample inspection: The officer inspects the on-board sample locker, checking seal integrity and chain-of-custody for the sample corresponding to the most recent bunker delivery and one or two earlier deliveries.
4. Sample test (selective): At the officer’s discretion, a sample is broken open (in the presence of the chief engineer) and a sub-sample is taken for flag-state laboratory analysis. The laboratory tests sulphur by ISO 8754 (XRF) and reports the result within 60-90 days. The Appendix VI procedure is applied to the result.
5. In-use or tank sample (where required): Where the on-board delivered sample is unavailable, broken-sealed, or the test result is contested, the officer may draw a fresh in-use sample (from the fuel supply line) or an onboard sample (from a tank) under the Reg 14.8 designation added by MEPC.305(73). A fresh tank sample is less probative than the manifold sample because the in-tank fuel has been mixed with previously bunkered fuel.

The verification chain for sulphur compliance is: supplier sample (retained 30-90 days) → on-board delivered sample (retained 12 months) → PSC sample (drawn at PSC inspection) → flag-state laboratory result (Appendix VI procedure). A consistent result across all four confirms compliance; a divergence at any stage is a Reg 14/Reg 18 deficiency.

Common PSC findings: missing BDN, broken seal, sulphur over-spec

PSC databases (Tokyo MoU, Paris MoU, USCG) record the following Reg 18 findings most frequently, ranked by approximate detention frequency:

• BDN missing or incomplete (deficiency code 18402): A BDN cannot be located on board for a recorded bunker delivery, or the BDN is present but missing one or more of the 15 required fields. This is the most common Reg 18 finding and accounts for approximately 30-40% of Reg 18 deficiencies in the Tokyo MoU records. A missing BDN is a detainable deficiency under most MoUs if it occurs in combination with other findings (e.g. inconsistent IAPP supplement) or if the missing BDN corresponds to fuel currently in the day tank.
• Sample missing or seal broken (deficiency code 18403): The on-board sample for a recorded bunker delivery cannot be located, or is found with a broken seal. Approximately 15-20% of Reg 18 deficiencies. A missing sample with a still-valid BDN is typically a survey condition rather than a detention; a broken seal is a more serious finding.
• Sulphur over-spec relative to BDN declaration (deficiency code 14402): The flag-state laboratory test result, as processed through the Appendix VI procedure, exceeds the applicable decision threshold. Approximately 10-15% of Reg 18 deficiencies, but these are typically detentions because they imply either a non-compliant fuel was supplied (supplier liability) or a non-compliant fuel was burnt (operator liability).
• Inconsistent BDN-IAPP supplement: The IAPP supplement records ECA-grade fuel for a transit, but the BDN shows non-ECA-grade fuel as the most recent delivery. Approximately 5-10% of findings.
• Flash point below 60 degrees C: Approximately 1-2% of findings; rare but a SOLAS-detainable deficiency.

The detention rate for Reg 18 deficiencies in the Tokyo MoU records is approximately 15-20%, somewhat lower than for Reg 13 NOx findings but higher than for Annex I Reg 17 Oil Record Book findings. Detention typically requires the deficiency to be cleared (replacement BDN obtained, replacement sample drawn, or flag-state appeal lodged) before the vessel is released.

Post-2020 0.50% sulphur cap impact on BDN accuracy

The IMO 2020 0.50% sulphur cap under Reg 14.1, entering into force on 1 January 2020, substantially raised the stakes of the BDN sulphur declaration. Pre-2020, the BDN sulphur was the basis for a 3.5% global cap and a 0.10% ECA cap; the 3.5% cap was rarely the binding constraint, and the 0.10% ECA cap applied only on transit through the four legacy ECAs. Post-2020, the 0.50% cap applies globally, and the BDN sulphur declaration is the primary evidence of compliance on every voyage.

The post-2020 transition exposed systematic supplier-side BDN inaccuracy in some jurisdictions. In the first half of 2020, third-party laboratory testing services (such as VPS, FOBAS, Bureau Veritas Marine Fuel) reported that approximately 5-10% of VLSFO deliveries had a measured sulphur content above 0.53% m/m (the 0.50% limit plus the approximate 0.59R allowance), with the BDN declaring 0.50% or below. The discrepancy was attributed to a combination of factors:

• Blending tolerance: Suppliers were blending VLSFO from a residual fuel base and a low-sulphur cutter stock (typically a marine gas oil or a vacuum gas oil), with the blend ratio targeted at 0.45-0.48% to leave a margin below the 0.50% limit. Blending variability could push individual batches above 0.50%.
• Sampling variability: The supplier’s lab sample (from which the BDN sulphur is derived) was not always representative of the actual delivery.
• Supplier malpractice: A small minority of suppliers were issuing BDNs with declared sulphur below 0.50% knowing the actual fuel was above.

The IMO and the major flag administrations responded with enhanced PSC sampling in 2020-2021, with several MoUs (Paris, Tokyo, USCG) increasing the proportion of inspections including a sample test from approximately 5% pre-2020 to approximately 20% in 2020. The enhanced sampling identified a number of supplier-side malpractice cases and led to supplier delistings in several jurisdictions.

By 2022-2023, the BDN-vs-sample discrepancy had stabilised at approximately 2-3% of deliveries, comparable to the historical SECA rate. The 2018 amendments under MEPC.305(73), which formalised the 0.05% absolute tolerance and the prima-facie supplier liability for over-spec fuel, are credited with the improvement.

Bunker supply chain: Singapore, Fujairah, Rotterdam, Hong Kong, Houston

The global bunker market is concentrated at a small number of major bunkering hubs, ranked by 2024 delivery volume:

• Singapore: approximately 54 million metric tonnes delivered in 2024, the largest bunker port globally for the past two decades. Singapore is the principal bunkering hub for the Asia-Pacific trade and for vessels transiting between East Asia and the Indian Ocean. The Maritime and Port Authority of Singapore (MPA) operates a tightly regulated bunker licensing regime, with mandatory mass-flow meters on all supplier barges from 2017 (residual) and 2019 (distillate).
• Fujairah, UAE: approximately 35-40 million tonnes in 2024, the second-largest hub, serving the Indian Ocean trade and the Persian Gulf. Fujairah’s bunkering activity grew rapidly post-2010 with the build-out of storage capacity at the port and is a frequent calling point for tankers and bulk carriers between the Middle East and East Asia.
• Rotterdam (ARA range): approximately 8-10 million tonnes at Rotterdam alone, and 15-18 million tonnes for the broader Antwerp-Rotterdam-Amsterdam (ARA) range. Rotterdam is the principal bunkering hub for the European trade and for vessels transiting between the Atlantic and the North Sea.
• Hong Kong: approximately 5-6 million tonnes in 2024, serving the South China and Pearl River Delta trade. Hong Kong’s bunker market shrank in the 2020s as Singapore captured share, but remains a significant regional hub.
• Houston / US Gulf: approximately 6-8 million tonnes in 2024, serving the US Gulf petrochemical trade and transatlantic vessels. The US Gulf is the principal bunkering hub for the Americas trade.
• Other notable hubs: Algeciras (Mediterranean), Las Palmas (Atlantic island), Panama (canal transit), Busan (South Korea), Tanger Med (Mediterranean / Africa).

The supplier registration regime under Reg 18 applies in all of these jurisdictions, with the supplier-side audit performed by the bunker port’s flag administration. Singapore and Rotterdam are widely regarded as the most rigorous jurisdictions for supplier registration; some smaller bunkering ports in West Africa, the Caribbean and parts of South America have weaker supplier-side enforcement, and operators are advised to rely on third-party fuel-quality testing (VPS, FOBAS, Bureau Veritas Marine Fuel) for deliveries from these jurisdictions.

BIMCO Bunker Clauses 2024 + charter-party allocation

The BIMCO Bunker Clauses 2024, published by the Baltic and International Maritime Council in February 2024, are the standard charter-party allocation regime for bunker quality, quantity and sulphur compliance. The 2024 clauses replaced the 2018 edition and are now the default reference in most time charter parties, voyage charter parties, and bareboat charters.

The 2024 clauses allocate the following responsibilities:

• The time charterer is responsible for bunker procurement and for BDN compliance under MARPOL Reg 18 (since the charterer instructs the supplier and signs the supply contract).
• The shipowner is responsible for bunker handling on board and for the on-board sample retention under Reg 18.8 (since the chief engineer signs the BDN as recipient).
• The shipowner indemnifies the time charterer for any on-board sulphur non-compliance arising from poor handling (e.g. fuel mixing in tanks).
• The time charterer indemnifies the shipowner for any delivered fuel sulphur non-compliance arising from supplier malpractice (e.g. BDN-vs-sample over-spec).
• PSC detention arising from a fuel-quality finding triggers the off-hire clause, with the off-hire period running from the detention to the release.
• The fuel-quality dispute is subject to the arbitration clause of the charter party, typically London (LMAA), New York (SMA) or Singapore (SCMA) arbitration.

The 2024 clauses also incorporate a FuelEU compliance clause, allocating the FuelEU compliance cost (the renewable share, the GHG intensity, and any FuelEU penalty) between the parties. The default allocation is that the time charterer bears the FuelEU compliance cost (since the charterer instructs the bunker fuel choice), with the shipowner bearing the MRV reporting cost (since the owner provides the operational data).

The 2024 clauses are the principal commercial instrument that translates the MARPOL Reg 18 BDN regime into charter-party contractual obligations, providing a coherent allocation chain from the supplier to the end charterer.

Bunker-quality dispute arbitration (IBIA + Court of Arbitration)

Bunker-quality disputes are typically resolved through one of three forums:

• LMAA (London Maritime Arbitrators Association) is the principal forum for bunker disputes governed by English law and is the default forum under the BIMCO clauses for many charter parties. LMAA bunker arbitrations typically run 12-24 months and produce binding awards enforceable internationally under the New York Convention.
• SCMA (Singapore Chamber of Maritime Arbitration) is the principal forum for bunker disputes arising in the Asia-Pacific bunker market, particularly Singapore-supplied fuel. SCMA bunker arbitrations are typically faster (8-18 months) and benefit from the close geographical link to the Singapore bunker market.
• IBIA-mediated commercial settlement: The International Bunker Industry Association (IBIA) operates a mediation service for bunker disputes at the commercial level (supplier-buyer), separate from the legal arbitration forums. IBIA mediation is non-binding but often produces settlements within 3-6 months at substantially lower cost than arbitration.

The principal technical evidence in a bunker-quality dispute is:

• The supplier sample (drawn at the supplier barge, retained by the supplier for 30-90 days).
• The manifold sample (drawn at the receiving ship’s manifold, retained on board for 12 months under Reg 18).
• The commercial sample (drawn at the manifold, retained on board for 30 days for charter-party purposes).
• The flag-state PSC sample (where a PSC inspection has occurred).
• The third-party laboratory test reports from VPS, FOBAS, Bureau Veritas Marine Fuel or equivalent.

The chain of custody under MEPC.250(66) is a critical evidential issue in arbitration: a sample with a broken seal or an incomplete chain-of-custody record is typically excluded from evidence, and the dispute is reduced to a contest between the supplier sample and any in-tank sample drawn later. The 2014 amendments are therefore not only a regulatory enforcement tool but also a commercial evidence-quality instrument.

Class society implementation: DNV, LR, ABS, BV, NK, RINA, KR, CCS, RS, IRS

The major IACS classification societies implement the Reg 18 BDN and sample regime through their flag-state recognised-organisation authority, with implementation guidance specific to each society:

• DNV (Det Norske Veritas) issues guidance through DNV-CG-0288: Bunker delivery note and fuel oil sample handling and through the DNV PS fuel-quality testing service. DNV’s implementation emphasises the continuous-flow sampler design at the manifold and the electronic chain-of-custody for samples.
• Lloyd’s Register (LR) issues guidance through the FOBAS Bunker Handbook and through the LR ShipRight fuel-management procedure. FOBAS is one of the principal third-party fuel-quality testing services and provides the third-party sample analysis that complements the on-board regulatory sample.
• ABS (American Bureau of Shipping) issues guidance through the ABS Fuel Conditioning and Testing Guide and through the ABS Nautical Systems on-board software for bunker management.
• Bureau Veritas (BV) issues guidance through the Bureau Veritas Marine Fuel testing service and through the BV Solution on-board software. BV’s service is widely used in the European bunker market.
• NK (ClassNK / Nippon Kaiji Kyokai) is the principal classification society in the Japanese-flag fleet and issues guidance through the NK Fuel Oil Quality Manual. NK is particularly active in the Tokyo MoU jurisdiction.
• RINA (Registro Italiano Navale) is active in the Mediterranean bunker market and issues guidance aligned with the Mediterranean SECA 2025 implementation.
• KR (Korean Register) is the principal classification society in the Korean-flag fleet and is particularly active in the LNG and methanol fuel markets, where the Reg 18 BDN must be supplemented by IGF Code documentation.
• CCS (China Classification Society) is the principal classification society in the Chinese-flag fleet and is active in the Hong Kong and Shanghai bunker markets.
• RS (Russian Maritime Register of Shipping) operates a parallel BDN registration system for Russian-flag vessels in Russian and former-Soviet bunker ports.
• IRS (Indian Register of Shipping) is active in the Indian and Sri Lankan bunker markets and provides Reg 18 compliance support for the Indian-flag fleet.

The IACS-level Common Procedural Requirement (PR) for bunker delivery note implementation is PR-39: Bunker Delivery Note Verification, issued in 2017 and revised in 2024 to incorporate the FuelEU Article 9 fields and the forthcoming Chapter 4 ter fields. PR-39 is the binding inter-society procedure that ensures consistent BDN review across all IACS members.

The Bunker Delivery Note as a discrete-requirement instrument

Regulation 18 imposes a set of discrete documentation and retention requirements rather than a continuous limit function. There’s no single governing equation; there is a small set of fixed quantities, each of which a chief engineer or a port state control officer can check against the document and the sealed bottle on board. The retained sample is fixed at one litre per delivery, held for 12 months: $V_{\text{sample,retained}} = 1\ \text{L}$ per delivery, retained 12 months. The BDN itself is retained for three years on board, $T_{\text{BDN,retention}} = 3\ \text{years}$. The declared sulphur must sit at or below the applicable cap, $c_{\text{S,BDN}} \leq c_{\text{S,cap}}$, where $c_{\text{S,cap}}$ is 0.50% m/m outside emission control areas (per Reg 14.1), 0.10% m/m in the legacy SECAs (Baltic, North Sea, North American, US Caribbean), and 0.10% m/m in the Mediterranean SECA from 1 May 2025.

These quantities are not derived from a model; they are the numbers MARPOL fixes. The interest is in how each one is calibrated against the operational reality it has to survive: a PSC inspection that lands months after the delivery, a flag-state laboratory that needs 60 to 90 days, and a supplier who may dispute the result.

The 3-year BDN retention is calibrated to the two-cycle PSC visit horizon plus the IAPP renewal survey horizon. Most vessels receive 2 to 3 PSC inspections per year, so a 3-year window covers 6 to 9 inspections. The 5-year IAPP renewal survey reviews the bunker history; the 3-year minimum lets the renewal surveyor read the most recent three years of bunker activity even where the BDN file has been transferred between management companies. The 3-year period is a floor, not a ceiling: many flag administrations and P&I clubs ask for the BDN to be kept for the life of the ship, and the marginal cost of a single retained page or PDF is near zero.

The flash-point and sulphur limits the BDN carries

The flash point under SOLAS Reg II-2/4.2 must be at least 60 degrees C by the Pensky-Martens closed-cup method (ISO 2719), $T_{\text{flash,min}} = 60\ ^\circ\mathrm{C}$. That 60-degree line is the flammability-to-combustibility boundary in the IMO maritime classification: a liquid with closed-cup flash above 60 degrees C can’t form a flammable vapour-air mixture under ambient marine engineering conditions and may be handled in standard fuel-oil tanks without inerting. A 0.10% ULSFO with a 55-degree flash is a SOLAS deficiency irrespective of its Reg 14 compliance.

The sulphur cap recorded on the BDN is the document’s load-bearing field. The supplier’s declaration in field 10 states conformity with paragraph 1 (0.50% global) or paragraph 4 (0.10% ECA) of Reg 14. That declaration is the legal hook: when a flag-state laboratory later tests the sealed sample, the test result is processed through the Appendix VI procedure and checked against the applicable decision threshold, not the bare cap.

The MARPOL fuel-oil sample and its volume budget

The 1-litre sample volume is calibrated to the sum of the test-method sample volumes. ISO 8754 (energy-dispersive XRF sulphur) needs roughly 250 ml for a triplicate determination with retention of duplicate aliquots; ISO 3675 (laboratory density by hydrometer) needs about 100 ml; ISO 2719 (Pensky-Martens flash) needs about 80 ml; and a retention aliquot of about 200 ml is held back for repeat analysis. The volume budget is therefore:

The 630 ml total sits comfortably below the 1-litre regulatory minimum, leaving about 370 ml of headroom for spillage and for testing beyond the 12-month window.

The 12-month sample retention is calibrated to the PSC plus flag-state laboratory turnaround. A typical PSC inspection occurs within 6 to 9 months of any given bunker delivery; the laboratory turnaround is 60 to 90 days; the two sum to roughly 8 to 12 months. The 12-month minimum ensures the sample is still available at the conclusion of the laboratory turnaround for any PSC inspection that lands within the year. The sample must be drawn by continuous flow at the receiving ship’s manifold and sealed at the time of drawing by the supplier in the presence of the chief engineer, per the MEPC.250(66) chain-of-custody rules set out earlier. Most operators keep samples for 24 months as a precaution, since some flag administrations have asked for historical samples in retrospective enforcement.

Verifying the sulphur result: Appendix VI in detail

When a flag-state laboratory tests the sealed sample, the result isn’t compared directly against the bare 0.50% or 0.10% figure. MARPOL Annex VI Appendix VI sets out the verification procedure for a fuel-oil sample, and that procedure adds a measurement allowance to the limit so that test-method uncertainty doesn’t by itself convict a compliant vessel.

The procedure works at a 95% confidence level. The MARPOL sample (the manifold-drawn, sealed, on-board sample) is tested in duplicate by the flag-state laboratory; the two results are averaged; and the averaged value V is judged against the specification limit. The acceptance rule is built on the reproducibility R of the test method: the procedure treats the fuel as meeting the limit if the measured value, allowing for 0.59R applied to the reproducibility, doesn’t exceed the specification limit. For the residual-fuel sulphur method at the 0.50% level, 0.59R is on the order of 0.012 to 0.018% absolute, so the effective decision threshold for a 0.50% limit lands near 0.53% and the threshold for a 0.10% ECA limit lands near 0.11%. The 0.59R term is the statistical heart of the procedure: it converts a single laboratory’s reproducibility into a one-sided 95%-confidence allowance so that a vessel is found non-compliant only when the measured sulphur exceeds the limit beyond the reach of test-method scatter.

The same Appendix VI procedure applies to in-use samples and onboard samples drawn under Reg 14.8; the applicable thresholds are the same (approximately 0.53% for the 0.50% cap, approximately 0.11% for the 0.10% ECA cap). The 0.05% BDN-vs-sample tolerance for prima-facie supplier liability sits alongside this: the supplier’s position is assessed by comparing the BDN-declared value against the sample-tested value, and a gap above 0.05% absolute shifts the liability burden to the supplier subject to flag-state appeal.

The supplier-side registration timeliness rule sits alongside the verification procedure: the supplier must register the BDN within 5 working days post-delivery, $T_{\text{registration}} \leq 5\ \text{working days}$, which is also the parallel obligation under FuelEU Article 9.

Worked example

A 12,000 TEU container ship bunkers 3,200 metric tonnes of VLSFO at Singapore on 5 May 2026 from a licensed supplier.

The supplier issues a BDN with all 15 fields completed: supplier name (Singapore Bunker Co Pte Ltd), receiving ship name and IMO number (MV Example, IMO 9999999), delivery port (Singapore), delivery date (5 May 2026), product name (VLSFO RMG-380 0.50%), quantity (3,200 mt), density at 15 degrees C (985.0 kg/m³), sulphur (0.46% m/m), flash point (95 degrees C), supplier declaration (Reg 14.1 0.50% conformity), other parameters (viscosity at 50 degrees C 380 cSt, water 0.2%, ash 0.05%), supplier signature, chief engineer signature, and BDN reference number BS-2026-0501-3200.

A continuous-flow drip sample is drawn at the receiving ship’s manifold throughout the 4-hour delivery. The 1-litre sample bottle is sealed at the manifold by the supplier representative in the presence of the chief engineer at 14:30 hrs on 5 May 2026, with seal serial number 9876543. The chain-of-custody label records the ship name, IMO number, port (Singapore), date (5 May 2026), BDN reference (BS-2026-0501-3200), seal serial (9876543), and both signatures. The sample is transferred to the on-board sample locker (engine room, port side, frame 78) at 15:00 hrs on 5 May 2026 by the third engineer, who logs the transfer in the bunker chain-of-custody log.

The BDN is filed in the chief engineer’s BDN binder under the May 2026 tab and is retained for 3 years (until 5 May 2029). The sample is retained in the sample locker for 12 months (until 5 May 2027).

A Tokyo MoU PSC inspection on 22 September 2026 (4.5 months post-delivery) reviews the BDN file, confirms the May 2026 BDN, inspects the on-board sample for the May 2026 delivery, confirms the seal is intact and the chain-of-custody label is complete, and decides not to draw the sample for testing (no other findings of concern). The inspection closes without deficiency.

In an alternative run, an October 2026 inspection at Yokohama draws the May 2026 sample for laboratory testing. The flag-state laboratory (Japan Coast Guard) reports a sulphur of 0.48% m/m on 12 December 2026 (60-day turnaround). Run through the Appendix VI procedure, 0.48% sits below the approximately 0.53% effective decision threshold for the 0.50% limit. The BDN-vs-sample gap is 0.02% (0.48% measured vs 0.46% declared), well within the 0.05% absolute tolerance. Both checks confirm compliance. The example shows the routine flow at a major bunkering hub: the BDN is the standing regulatory document, the sample is the contingent evidence that backs it if challenged, and the supplier registration is the parallel audit trail at the bunkering port.

Limitations

The Reg 18 regime is a documentary and evidential chain, not a direct measurement of what the engine burns, and several limitations follow from that.

The first limitation is the gap between BDN-declared quality and actual delivered quality. The BDN-declared sulphur is derived from the supplier’s own laboratory sample, which is assumed representative of the delivered fuel; the MEPC.250(66) manifold-sample requirement is the only regulatory anchor for that assumption. In the first half of 2020, third-party testing services reported that 5 to 10% of VLSFO deliveries measured above 0.53% m/m while the BDN declared 0.50% or below, a figure that settled to 2 to 3% by 2022 to 2023. The document is only as honest as the sample it rests on.

The second limitation is the distinction between in-use, onboard, and delivered samples. The MARPOL manifold sample captures the fuel as delivered; the in-use sample (drawn from the engine fuel-supply system) and the onboard sample (drawn from a tank) capture fuel that has been blended with a residual heel of older fuel. Where the day tank is fed from a service tank holding mixed fuel, BDN attribution becomes uncertain, and a fresh in-tank sample drawn by a PSC officer is less probative than the manifold sample because the in-tank fuel is no longer a clean record of any single delivery.

The third limitation sits in the verification thresholds themselves. The Appendix VI 0.59R reproducibility allowance produces an effective decision threshold near 0.53% for a 0.50% limit and near 0.11% for a 0.10% ECA limit; the often-quoted 0.50% and 0.10% caps are the specification limits, not the figures a laboratory result is convicted against. Reading the bare cap without the verification allowance overstates how tight the enforced boundary is, and treating the ISO 8217 grade as the regulatory benchmark compounds the error: a 3.0% RMG-380 is on-spec to the ISO grade yet non-compliant with the 0.50% cap.

The fourth limitation is enforcement variation. The fuel oil non-availability report (FONAR) under MEPC.1/Circ.878 lets a vessel record that compliant fuel couldn’t be obtained, but FONAR acceptance and follow-up differ markedly between flag and port states, and the FONAR doesn’t replace the BDN: the BDN must still be issued for the non-compliant fuel actually delivered. Supplier-side registration is rigorous in Singapore and Rotterdam and weaker in some smaller ports, so the audit trail that the regime assumes is not uniformly present.

A final limitation is that several figures in this article are estimates or ranges rather than fixed regulatory constants. The 250, 100, 80, and 200 ml test-method volumes are typical laboratory practice, not MARPOL-mandated quantities; the 0.59R coefficient and the resulting decision thresholds depend on the reproducibility of the specific test method and edition in force; and the deficiency-frequency percentages reflect historical PSC database snapshots that move year to year. Treat them as working approximations for planning, and confirm the controlling figures against the current resolution text before relying on them in a dispute.

Regulatory basis

The numbers above rest on a defined set of instruments: MARPOL Annex VI Regulation 18 (BDN content, retention, sample, supplier registration); MARPOL Annex VI Appendix V (the BDN minimum-content schedule, 15 fields); MARPOL Annex VI Appendix VI (the fuel-oil-sample verification procedure with the 0.59R, 95%-confidence rule, added by MEPC.305(73)); Resolution MEPC.176(58) (2008 amendments establishing the modern Reg 18 regime); Resolution MEPC.250(66) (2014 amendments specifying spot-sample location and sealing protocol); Resolution MEPC.305(73) (2018 amendments: Reg 14.8 sampling points, Appendix VI verification procedure, 0.05% absolute BDN-vs-sample tolerance); Resolution MEPC.182(59) (2009 Guidelines for Fuel Oil Sampling); the 2019 consistent-implementation guidance MEPC.1/Circ.881; SOLAS Regulation II-2/4.2 (60-degree minimum flash point for main-propulsion fuel); ISO 8217:2024 (the marine fuel commercial-quality specification, parallel to Reg 18); Regulation (EU) 2023/1805 Article 9 (the FuelEU Maritime parallel BDN); and the MEPC 83 outcome of April 2025 (the IMO Net-Zero Framework Chapter 4 ter, forthcoming).

Common operator errors

A handful of mistakes recur on board and in the supply chain. Operators treat the BDN as a commercial document only, when it is a regulatory document under Reg 18 whose obligation is independent of the supply contract. They equate the ISO 8217 grade with the Reg 14 cap, when a fuel on-spec to RMG-380 at 3.0% sulphur is non-compliant with the 0.50% global cap. They draw a batch sample at the start, middle, or end of a delivery instead of a continuous-flow sample at the manifold, which is not Reg-18-compliant. They dispose of the sample before 12 months or the BDN before 3 years, each a Reg 18 deficiency. They confuse the FONAR with the BDN, forgetting that a vessel filing a FONAR still receives a BDN for the non-compliant fuel actually delivered. They overlook the FuelEU Article 9 BDN for EU calls, which forfeits the renewable benefit and defaults the fuel to fossil values. They overlook the BIMCO Bunker Clauses allocation, which can shift the cost of a non-compliance between owner and charterer even where Reg 18 is satisfied. And they read the 3-year BDN retention as a ceiling rather than the floor it is.

See also

• MARPOL Annex VI: parent annex (air pollution)
• MARPOL Annex VI Regulation 13: NOx Tier I, II, III: companion air-pollution regulation
• IMO 2020 sulphur cap: Reg 14 sulphur regime, the principal user of the BDN sulphur declaration
• MARPOL Convention: top-level treaty
• Baltic Sea SECA + NECA
• North Sea SECA + NECA
• FuelEU Maritime intensity formula breakdown: EU regional GHG-intensity regime, parallel BDN under Article 9
• IMO GFS methodology: global GHG-fuel-intensity regime, forthcoming parallel BDN under Chapter 4 ter
• Per-fuel WTW: VLSFO and MGO
• Per-fuel WTW: HFO
• Per-fuel WTW: LNG Otto vs diesel
• MARPOL Annex I Regulation 17: Oil Record Book: companion documentation regulation
• Calculator catalogue

Related calculators

• Tanker Op - Bunker delivery note
• MARPOL Annex VI/7 - Duration of certificate
• MARPOL Annex VI/6 - IAPP certificate
• MARPOL Annex VI/5 - Survey and certification
• MARPOL Annex VI/28 - CII
• MARPOL Annex VI/27 - Data collection system
• MARPOL Annex VI/26 - SEEMP revised
• MARPOL Annex VI/25 - EEXI