Bunker Quality and ISO 8217 Marine Fuel Standards

Bunker fuel quality is one of the costliest variables in ship operations. A single off-spec stem can mean six-figure engine damage, port detention, and months of dispute correspondence. ISO 8217, now in its sixth edition (2024), is the contractual bedrock: it defines which parameters matter, what the limits are, and which test methods apply. MARPOL Annex VI Reg 18 layers a regulatory sampling regime on top. Together they govern every metric tonne of fuel exchanged at sea.

This article covers the full technical framework: the grade structure, the key parameters and their limits, the test methods behind each one, VLSFO-era stability problems, catalytic fines, the CCAI ignition index, the MARPOL sampling regime, and the mechanics of a bunker dispute. The companion calculator ISO 8217 Parameter Check lets you screen a lab certificate against the standard’s limits directly, and the voyage bunker cost calculator prices the tonnes the quality battle is fought over.

ISO 8217: scope and edition history

ISO 8217 is published by the International Organization for Standardization under Technical Committee 28 (Petroleum and related products). It carries the formal title “Petroleum products, Fuels (class F), Specifications of marine fuels.” The 2017 edition (fifth edition, ISO 8217:2017) is the one most BDNs and supply contracts reference; the 2024 edition (sixth edition, ISO 8217:2024) tightened several parameters, revised the treatment of bio-derived components, and introduced new table structures for blended fuels. Not all supply contracts have yet migrated to the 2024 edition, so confirming which edition applies is the first step in any quality assessment.

The standard’s scope is straightforward: it specifies the minimum quality characteristics of fuels intended for use in marine diesel engines, marine gas turbines, and boilers before shipboard treatment (heating, purification, filtration). It does not cover liquefied gases (LNG, LPG), ammonia, methanol, or hydrogen; those alternative fuels have separate or emerging standards.

ISO 8217 has gone through six editions: 1987, 1996, 2005, 2010, 2017, and 2024. Each edition has tightened limits as engine technology, environmental regulation, and refinery practices evolved. The most operationally significant jumps were the 2010 edition (added CCAI, tightened hydrogen sulphide to 2.00 mg/kg), the 2017 edition (tightened cat fines from 80 to 60 mg/kg, added acid number, oxidation stability, and microbiologically influenced contamination provisions), and the 2024 edition (added bio-blend tables, revised the handling of fatty acid methyl ester (FAME) content, and aligned with VLSFO operational experience post-IMO 2020).

Distillate grades (Class DM)

ISO 8217 divides marine fuels into two classes by origin: distillate (Class DM) and residual (Class RM). The distillate class covers fuels produced by distillation, free from residual blending stock.

ISO 8217:2017 defines four distillate grades:

DMX is the lightest grade, intended for small craft, emergency generators, and applications requiring cold-flow performance. Flash point minimum is 43 deg C (lower than the 60 deg C SOLAS minimum, so DMX is restricted from use in ship machinery spaces except emergency engines). Kinematic viscosity range: 1.40 to 5.50 cSt at 40 deg C. Cetane index minimum: 45.

DMA is the standard marine gas oil, the most widely traded distillate grade. Flash point minimum 60 deg C; kinematic viscosity 1.50 to 6.00 cSt at 40 deg C; maximum sulphur 1.00% (with the MARPOL cap of 0.10% applying in ECAs, and the 0.50% global cap applying outside); density maximum 890 kg/m3 at 15 deg C; cetane index minimum 40.

DMZ matches DMA in most parameters but requires a tighter cetane index minimum of 40 (the ISO 8217:2010 edition raised this from 35, and the 2017 edition maintained it). DMZ is effectively premium MGO, typically specified for high-speed four-stroke engines that need reliable ignition.

DMB is a heavier distillate grade that permits limited residual content. Flash point minimum 60 deg C; kinematic viscosity 2.00 to 11.00 cSt at 40 deg C; cloud point and cold filter plugging point not specified (unlike DMA/DMZ, which carry cold-filter limits). DMB has become a minority grade: most operators have moved to DMA or a blended VLSFO for residual applications.

The distillate grades are the fuels of ECA operation. Any ship entering an ECA (North Sea, Baltic, North American, US Caribbean) must switch to fuel with sulphur content at or below 0.10% mass/mass. DMA-grade MGO routinely delivers at 0.05 to 0.08% sulphur, well within compliance. The ISO 8217 Parameter Check calculator includes DMA and DMZ limit tables for lab-certificate screening.

Residual grades (Class RM)

Residual fuels derive from the heavy bottoms remaining after atmospheric and vacuum distillation of crude oil. They’re cheaper per gigajoule than distillate but require heating, purification, and careful handling.

ISO 8217:2017 organizes residual grades along two axes: a viscosity letter (A, B, D, E, G, K) and a nominal kinematic viscosity at 50 deg C in cSt (10, 30, 80, 180, 380, 500, 700). The notation system concatenates them: RMG 380 means Residual, class M, viscosity letter G, nominal 380 cSt.

The grade table from ISO 8217:2017 (Table 2) covers:

RMG 380 has been the dominant bunker product for large slow-speed two-stroke engines on ocean-going vessels for decades. RMK grades (density up to 1010 kg/m3) are used in regions where refineries produce heavier crude streams.

The 2024 edition revised this table structure to accommodate biofuel blends. ISO 8217:2024 introduced a separate table (Table 4) for distillate grades with FAME content up to 7% v/v (B7), aligning with the EN 590 biodiesel blend standard used in road fuels, and a separate annex for higher biofuel content.

Key parameters, limits, and test methods

ISO 8217 imposes limits on approximately 20 parameters per grade. The following are the operationally critical ones, each with its test method and the physical reason the limit exists.

Density at 15 deg C

Test method: ISO 3675 (hydrometer, crude method) or ISO 12185 (oscillating U-tube, more precise). Units: kg/m3. Limits: DMA 890.0 max; RMG 380 and RME 180 991.0 max; RMK grades 1010.0 max.

Density matters for three reasons. First, it’s the primary parameter for mass calculation: bunkers are measured volumetrically at delivery temperature, then converted to metric tonnes using the volume correction factor (VCF) from ASTM D1250 / ISO 91-1 tables. A density error of 5 kg/m3 on a 1,000-tonne stem introduces a 5-tonne mass error. Second, the centrifugal purifier separates water and solids from fuel based on density difference; water at 1000 kg/m3 can’t be separated from fuel above 991 kg/m3 without heating to expand the separation margin. The purifier’s gravity disc must be selected to match the fuel density. Third, density combined with kinematic viscosity gives the CCAI. The bunker density-temperature correction calculator handles VCF conversion from delivery temperature to 15 deg C reference.

Kinematic viscosity at 50 deg C

Test method: ISO 3104 (glass capillary viscometer). Units: mm2/s (= cSt). Limits: grade-specific upper bounds (10, 30, 80, 180, 380, 500, or 700 cSt per nominal grade).

Viscosity determines the fuel injection system requirements. Residual fuel must be heated to reduce viscosity to the injection target (typically 10 to 15 cSt at the fuel injection pump inlet). A Walther viscosity-temperature relationship governs this, and the ship’s fuel heaters are sized accordingly. Over-viscous fuel at injection starves atomization, causing poor combustion. Under-viscous fuel (from over-heating or from using a lower-grade fuel in a system sized for heavy oil) causes injection pump wear through reduced lubricity. The bunker viscosity-temperature calculator applies the Walther equation to find the heater temperature needed for a target injection viscosity given the fuel’s measured viscosity at 50 deg C.

Sulphur content

Test method: ISO 14596 (wavelength-dispersive X-ray fluorescence, WDXRF; the most precise, used for compliance determination) or ISO 8754 (energy-dispersive XRF, ED-XRF; faster, used for screening). Units: percent mass/mass.

MARPOL Annex VI Reg 14 sets the global cap at 0.50% m/m (since 1 January 2020) and 0.10% m/m inside ECAs. ISO 8217:2017 sets no sulphur limit for grades above DMA; MARPOL is the binding constraint. ISO 14596 is the reference method for dispute resolution; if the BDN’s declared sulphur and the ISO 14596 result disagree, ISO 14596 governs. The sulphur compliance check implements the ISO 14596 calculation framework.

The MARPOL BDN sulphur declaration is the supplier’s warranty. If ISO 14596 analysis of the MARPOL sample shows sulphur above the declared value plus measurement uncertainty (typically 0.03% absolute for XRF), the supplier is in breach. PSC officers can detain a ship if the MARPOL sample or the onboard fuel tests outside compliance.

Carbon residue (Micro CCR)

Test method: ISO 10370 (micro method; replaces the older Conradson method for marine fuel analysis). Units: percent mass. Limits: 2.50% for RMA 10, up to 20.00% for RMK grades.

Carbon residue predicts the tendency of a fuel to form carbonaceous deposits on piston crowns, exhaust valves, and injector tips. It correlates with the asphaltene content and with refinery process severity. High micro CCR fuels require careful combustion management and cylinder oil dosing to prevent deposit buildup and cold corrosion. The micro carbon residue calculator screens lab values against ISO 8217 grade limits.

Total sediment potential (TSP)

Test methods: ISO 10307-1 (TSP by hot filtration, existent sediment) and ISO 10307-2 (TSP after aging, aging stability). Units: percent mass. ISO 8217:2017 limit: 0.10% for residual fuels (both existent and aged).

Sediment indicates asphaltene instability. TSP by ISO 10307-2 is the accelerated aging test that mimics what happens to the fuel during a long voyage: the sample is heated to 100 deg C for 24 hours, then filtered. If sediment exceeds 0.10%, the fuel is unstable and will drop asphaltene sludge during storage. This is the test most associated with post-IMO 2020 VLSFO failures.

Ash content

Test method: ISO 6245. Units: percent mass. ISO 8217:2017 limit: 0.100% for all residual grades.

Ash is the non-combustible mineral residue. High ash indicates contamination with metallic compounds (sodium, calcium, vanadium, silicon) that cause high-temperature corrosion of exhaust valves and turbocharger blades. Vanadium in particular forms low-melting-point eutectics with sodium that attack valve seats at temperatures above about 550 deg C.

Catalytic fines (Al + Si)

Test methods: ISO 10478 or IP 501 (gravimetric ICP-OES methods for aluminium and silicon). Units: mg/kg combined Al + Si. ISO 8217:2017 limit: 60 mg/kg for all residual grades (tightened from 80 mg/kg in ISO 8217:2010).

Catalytic fines are micro-particulates of aluminium silicate, the residue from fluidized catalytic cracking (FCC) units used in high-conversion refineries. Individual cat-fine particles range from 5 to 30 microns in diameter, hard enough (Mohs hardness 7, comparable to quartz) to abrade fuel injection equipment and cylinder liners. The 60 mg/kg ISO 8217 delivery limit is not an engine-inlet limit. Engine builders typically specify 10 to 15 mg/kg at the injector inlet; MAN ES specifies 15 mg/kg maximum at the engine inlet in their operating manuals. The difference between 60 mg/kg at delivery and 15 mg/kg at the engine depends on the purification train: typically two centrifugal separators in series, operated at the correct temperature and with correctly sized gravity discs.

Cat fines are one of the most frequent bunker dispute topics. Heavy fuel oil from refineries with FCC units (common in Asian and European refinery centres) can carry 80 to 100+ mg/kg at the point of production. Blending and settling reduce the value before sale, but deliveries exceeding 60 mg/kg are not rare. Engine damage from cat fines can exceed $500,000 for a complete liner replacement on a large slow-speed two-stroke.

Water content

Test method: ISO 3733 (Karl Fischer titration for distillate fuels) or distillation/centrifuge for residual fuels. Units: percent volume. ISO 8217:2017 limits: 0.30% for distillate grades; 0.50% for residual grades.

Water in fuel causes corrosion in storage tanks, promotes microbial growth, and risks flame-out if injected as a slug. Water in residual fuel above the purification system’s design capacity can cause flameouts in boilers. Water above 0.50% in residual fuel is grounds for rejection; it normally indicates either condensation during storage or deliberate addition to inflate volume (bunker fraud).

Flash point

Test method: ISO 2719 (Pensky-Martens closed-cup method). Units: degrees Celsius. ISO 8217:2017 minimum: 60 deg C for all DMA, DMZ, DMB, and all RM grades used in machinery spaces. DMX permits a minimum of 43 deg C.

SOLAS Chapter II-2 Regulation 4 requires that fuel used in ship machinery spaces (boilers, main engines, generators) must have a minimum flash point of 60 deg C. A flash point below 60 deg C means the fuel produces flammable vapour at or above ambient temperature, creating an explosion risk in the engine room. Flash point below 60 deg C is the one ISO 8217 parameter exceedance that requires immediate rejection and off-loading regardless of commercial implications.

Hydrogen sulphide (H2S)

Test method: IP 570 (headspace analysis). Units: mg/kg. ISO 8217:2017 limit: 2.00 mg/kg for all residual grades.

H2S is a toxic gas (IDLH 50 ppm by NIOSH). High H2S in bunker fuel can off-gas during tank opening or transfer, creating life-safety hazards for crew and terminal workers. The 2.00 mg/kg limit was first introduced in ISO 8217:2010 after several incidents involving H2S exposure during bunker operations.

Acid number

Test method: ISO 6618. Units: mg KOH/g. ISO 8217:2017 limit: 2.5 mg KOH/g for all grades.

Acid number measures organic and inorganic acidity. High acidity indicates chemical contamination (such as strong acid carryover from refinery processes) or oxidation degradation. Acidic fuel causes corrosion in copper and copper-alloy fuel system components.

Oxidation stability

Test method: ISO 12205 (oxidation stability of distillate fuels) or ISO 15030 (oxidation stability of residual fuels). Units: g/m3 insolubles. Introduced in ISO 8217:2017 for distillate grades (maximum 25 g/m3 for DMA and DMZ). Residual grade oxidation stability is addressed via TSP (ISO 10307-2).

Oxidation stability measures the tendency of distillate fuel to form gums and peroxides on aging. This became relevant post-IMO 2020 because low-sulphur MGO intended for ECA operation was often stored for extended periods before use, and marginal-stability product degraded in service.

The CCAI ignition index

The Calculated Carbon Aromaticity Index (CCAI) is not a laboratory measurement; it’s a derived value calculated from density and kinematic viscosity. The formula is:

where $\rho_{15}$ is density at 15 deg C in kg/m3 and $\nu_{50}$ is kinematic viscosity at 50 deg C in cSt.

CCAI predicts ignition delay: a fuel that is highly aromatic (low hydrogen content, high density for its viscosity) ignites more slowly after injection, pushing the combustion event later in the cycle. ISO 8217:2017 sets a maximum CCAI of 870 for all residual grades. Engine builders typically require CCAI below 850 for optimal performance; some older engines specify maximum 840.

CCAI values above 870 indicate a fuel that may cause knocking, incomplete combustion, injector fouling, and exhaust valve burning. The index was developed in the 1980s by SINTEF and Shell as a practical proxy for ignition quality that could be derived from the two parameters already measured on every lab certificate. It doesn’t replace bench-engine testing, but it provides an immediate flag for problematic fuel. The CCAI calculator computes CCAI from a density and viscosity pair and rates it against the ISO 8217 limit.

VLSFO: stability and compatibility challenges post-IMO 2020

The IMO 2020 sulphur cap (MARPOL Annex VI Reg 14, effective 1 January 2020) required ocean-going ships burning residual fuel outside ECAs to switch from HFO (typically 2.5 to 3.5% sulphur) to fuel at or below 0.50% sulphur. This created the VLSFO market: refiners began producing 0.50% S fuels by blending low-sulphur vacuum gasoil, deasphalted oil, or hydroprocessed residuals with varying proportions of atmospheric residue and cutter stock.

VLSFO does not have a dedicated ISO 8217 grade designation. Products sold as VLSFO are typically labeled against an existing residual grade (often RMG 380 or RMD 80) plus the sulphur declaration. The problem is that VLSFO blends can have very different colloidal chemistry depending on the blend stocks used.

Traditional HFO at 3.5% sulphur had relatively consistent asphaltene chemistry because most of the blend stock was straight-run atmospheric residue from similar crude types. VLSFO blends vary enormously: a Rotterdam VLSFO from one refinery might mix deasphalted oil with vacuum gasoil, while another uses hydrocracker bottoms with cutter stock. When these two VLSFOs are commingled in a ship’s bunker tank, the asphaltene fraction from one can destabilize in the paraffinic environment of the other, precipitating as sludge.

ISO/PAS 23263:2019, titled “Petroleum products, Fuels (class F), Considerations for fuel suppliers and users regarding marine fuel quality in view of the implementation of maximum 0.50% m/m sulphur limit,” was developed specifically to address this. It introduced guidance on:

• Total sediment potential testing per ISO 10307-2 as the primary stability screen
• Compatibility testing before commingling
• Attention to wax appearance temperature (WAT) for VLSFO blends with high paraffinic content
• CCAI screening for VLSFOs (some had elevated CCAI from aromatic blend stocks used to meet density targets while cutting sulphur)

ISO 8217:2024 incorporated lessons from the 2020 to 2024 VLSFO operating period. It revised Table 2 to address bio-blend content, aligned the TSP limits with operational experience, and strengthened the oxidation stability requirements for distillate-heavy blends.

The spot compatibility test

The spot test (ASTM D4740, Standard Test Method for Cleanliness and Compatibility of Residual Fuels by Spot Test) is the field-rapid compatibility screen. A drop of the proposed mixture is placed on a filter paper and allowed to spread for 24 hours. A stable fuel produces a uniform dark disc. An incompatible mixture shows a dark central spot ringed by a lighter halo of separated oil, with a visible boundary where the asphaltenes have precipitated.

The spot test is not an ISO 8217 test method and doesn’t appear in the standard’s tables. But it’s the practical first-pass tool used by bunker surveyors and chief engineers before commingling a new stem with existing tank contents. A positive (incompatible) spot test result triggers a full ASTM D4740 or ISO 10307-2 lab test before any commingling proceeds. The voyage blend compatibility calculator supports this screening workflow.

MARPOL Annex VI: the regulatory fuel quality framework

ISO 8217 is a commercial specification standard. MARPOL Annex VI Regulations 14 and 18 are binding international treaty obligations that overlay and extend it.

MARPOL Annex VI Regulation 14: sulphur content

Reg 14 sets the maximum sulphur content of fuel oil used on board:

• 0.50% m/m global limit outside ECAs (since 1 January 2020, per the 2016 MEPC decision at MEPC.70)
• 0.10% m/m limit inside Emission Control Areas designated under MARPOL Annex VI Appendix III

An additional provision under Reg 14 requires fuel oil for use outside an ECA not to exceed 0.50% m/m sulphur content. This is enforced through flag state and port state control (PSC) inspection; PSC officers can demand the BDN and MARPOL sample for analysis.

MARPOL Annex VI Regulation 18: fuel oil quality

Reg 18 establishes the quality assurance regime independent of sulphur. Key provisions:

Fuel oil quality obligation (Reg 18.3): The fuel oil shall meet, at a minimum, the requirements of the BDN, including any applicable requirements of MARPOL Annex VI. The flag state requires ships to carry bunker fuel that meets the parameters declared on the BDN.

Bunker Delivery Note (Reg 18.5 and Appendix V): Every bunker delivery must be documented by a BDN issued by the fuel supplier. The BDN must declare: ship name and IMO number, port of bunkering, date, name and address of supplier, product name, quantity (mt), density at 15 deg C, sulphur content, and a statement that the fuel meets the applicable MARPOL requirements. The BDN must be retained on board for at least three years.

Representative sample (Reg 18.8): The supplier must deliver a representative sample sealed in the presence of the ship’s officer. The ship retains the sample for at least 12 months from the delivery date or until the bunker is substantially consumed, whichever is later. The sample is the primary evidence in any subsequent dispute or PSC inspection.

In-use and on-board samples (Reg 18.8.1): In addition to the MARPOL retained sample, port state inspectors may take in-use samples from the fuel in service during an inspection. These samples, analyzed per the protocols in MEPC.182(59), are the on-the-spot compliance evidence.

MEPC.182(59): bunker sampling guidelines

IMO Resolution MEPC.182(59), adopted in 2009, provides the detailed sampling procedure that Reg 18 requires:

• Sampling must be continuous drip-feed throughout the entire transfer, not a grab sample at start or end
• The sampler must be installed at the ship’s manifold connection point (not on the bunker barge or terminal side)
• Sample volume must be sufficient for replicate testing (minimum 1 to 4 litres, depending on the analyses required)
• Four sealed samples are typically drawn from one sampler: one retained by the ship (MARPOL sample), one to the supplier, one to the master’s custody, and optionally one to a third-party laboratory
• The sample seal must be signed by both ship’s officer and supplier representative

Disputes over sampling procedure (poorly sited sampler, grab sampling substituted for continuous drip, sample not co-signed) can undermine the evidentiary value of the MARPOL sample in arbitration. The bunker sampling procedure calculator supports the chief engineer in verifying procedural compliance before, during, and after bunkering.

The Bunker Delivery Note in detail

The BDN is both a commercial document and a MARPOL regulatory record. Under MARPOL Annex VI Appendix V, the mandatory fields are:

1. Name and IMO number of the receiving ship
2. Port of delivery
3. Date of commencement of delivery
4. Name, address, and telephone number of the fuel oil supplier
5. Product name(s)
6. Quantity in metric tonnes
7. Density at 15 deg C (kg/m3)
8. Sulphur content (% m/m)
9. A signed declaration that the fuel oil supplied conforms with the applicable MARPOL requirements

The density figure on the BDN is the supplier’s density measurement, not a certified lab value. Disputes arise when the BDN density and the ship’s own measurement differ: a 5 kg/m3 difference on 1,000 tonnes creates a 5-tonne mass discrepancy. These quantity disputes are separate from quality disputes but often arise simultaneously.

The chief engineer must sign the BDN to acknowledge receipt. Signing the BDN doesn’t waive quality claims; the standard endorsement is “Quality and quantity subject to independent verification.” The bunker delivery note reference page covers the document requirements in detail. The related MARPOL-specific regime for BDN records is covered in MARPOL Annex VI Reg 18.

ISO test methods: the measurement layer

ISO 8217 is a specifications standard; the actual measurements are performed per separate ISO and IP test methods. The key ones and their roles:

ISO 3675 / ISO 12185 (density): ISO 3675 uses a calibrated glass hydrometer, sufficient for most operational determinations. ISO 12185, using an oscillating U-tube densitometer, gives a precision of ±0.2 kg/m3 and is the reference method for dispute resolution. The density measurement calculator implements the ISO 12185 correction procedure.

ISO 3104 (kinematic viscosity): Glass capillary viscometer, calibrated with certified reference materials. Precision at 50 deg C for residual fuels is typically ±1% for repeat measurements by the same operator. The viscosity test calculator supports this calculation.

ISO 10370 (micro carbon residue, Micro CCR): The micro method requires only 0.5 to 1.0 g of sample, far less than the original Conradson method, and delivers precision comparable to the macro test.

ISO 10307-1 / ISO 10307-2 (total sediment): Part 1 measures existent sediment (no aging); Part 2 measures sediment after accelerated thermal aging at 100 deg C for 24 hours. Part 2 is the VLSFO stability test. The TSP calculators implement both.

ISO 14596 (sulphur by WDXRF): Wavelength-dispersive XRF gives the lowest uncertainty of the XRF methods, typically ±0.003 to 0.005% absolute for the 0.10 to 0.50% range. It is the reference method under MARPOL for dispute resolution. The sulphur test calculator covers the ISO 14596 measurement procedure.

ISO 3733 (water content): Karl Fischer titration for distillate fuels; centrifuge/distillation methods for residuals. ISO 3733 is the reference for water content in all marine fuel dispute contexts. The water content test implements this calculation.

ISO 10478 / IP 501 (catalytic fines): Both methods use ICP-OES to determine aluminium and silicon concentrations separately; the combined Al + Si value is compared to the 60 mg/kg ISO 8217 limit.

ISO 2719 (flash point): Pensky-Martens closed cup; the standard method for flash point determination across the marine fuel grade range. Minimum precision: ±1 deg C repeatability at the 60 deg C compliance threshold.

These test methods are the technical backbone of every bunker quality dispute. A dispute claim without reference to the applicable test method is incomplete.

Bunker dispute mechanics

Off-spec bunker disputes follow a predictable sequence, regardless of the nature of the deficiency:

Step 1: Quality claim trigger. The ship’s own tests (onboard viscosity check, density check, or rapid sulphur analyser) or engine performance anomalies (abnormal combustion, injector fouling, filter blockage) identify a potential deficiency. The chief engineer notifies the master and the shipowner’s technical department.

Step 2: MARPOL sample dispatch. The retained MARPOL sample is dispatched under seal to an accredited laboratory for analysis against the full ISO 8217 parameter table. The sample must be analyzed by the same methods as the supplier’s certificate to allow direct comparison.

Step 3: Letter of protest. A formal letter of protest is addressed to the bunker supplier, noting the deficiency claim and reserving all rights. The letter typically specifies which BDN parameters are disputed and what analysis has been commissioned.

Step 4: Counterclaim and supplier sample analysis. The supplier analyzes their retained sample (often a different laboratory). If the results differ materially, a third-party referee laboratory analysis of the ship’s MARPOL sample is commissioned, using the referee method specified in ISO 8217 (typically ISO 14596 for sulphur, ISO 12185 for density, and ISO 10478 for cat fines).

Step 5: Arbitration or settlement. Most disputes settle commercially: the supplier credits the cost of the affected fuel, the cost of engine repairs attributable to the deficiency, and agreed demurrage if the vessel had to deviate. Disputed cases go to arbitration under the applicable charter party or supply contract. The LMAA in London is the most common forum for English-law contracts; SCMA in Singapore handles Asia-Pacific disputes.

Cat fines disputes deserve a specific note. The ISO 8217 limit of 60 mg/kg applies at delivery (the BDN sample). If the ship’s analysis finds 80 mg/kg on the MARPOL sample but the supplier’s sample shows 58 mg/kg, the supplier will argue that their product was within specification and that the ship’s sampling point or procedure introduced contamination. The MARPOL sample at the ship manifold is the authoritative sample; if the sampler was correctly installed and operated, it wins the dispute. If the sampler was a temporary or non-compliant installation, the evidentiary chain is compromised.

Off-spec fuel and the FONAR

If a ship can’t obtain compliant fuel at a port (zero-sulphur fuel unavailable, or the only available fuel fails ISO 8217 on a critical parameter), the ship must file a Fuel Oil Non-Availability Report (FONAR) with the port state authority before departing. The FONAR documents the attempt to obtain compliant fuel, the names and responses of the suppliers contacted, and the decision to depart with non-compliant or limited fuel. A FONAR filed promptly limits the ship’s regulatory exposure; an after-the-fact FONAR provides much weaker protection. The FONAR and BDN documentation article covers the FONAR procedure in detail, and the bunker FONAR sulphur calculator helps quantify the exposure.

Fuel testing services and the FOBAS context

Several commercial fuel testing services provide bunker quality analysis. ISO 8217 itself doesn’t specify any particular laboratory or service; it specifies the test methods. When selecting a laboratory for dispute analysis, the key criteria are:

• Accreditation to ISO/IEC 17025 (General Requirements for the Competence of Testing and Calibration Laboratories) for the specific test methods in question
• Proficiency testing participation (round-robin programs run by CIMAC or national standards bodies)
• Sample custody chain: the laboratory must be able to certify that the MARPOL sample seal was intact on receipt

The IMO’s framework doesn’t endorse commercial testing services by name. The BIMCO Bunker Terms 2018 clause on sampling specifies only that the referee laboratory must be “mutually agreed or, in the absence of agreement, appointed by the competent authority in the port of delivery.”

ISO 8217:2024: the sixth edition changes

ISO 8217:2024 (sixth edition) was published in 2024 as an evolution from the 2017 fifth edition. Key changes include:

Biofuel blend tables. The 2024 edition added Table 3 for distillate blends containing FAME (fatty acid methyl esters) at up to 7% v/v, and Table 4 for distillate blends containing Hydroprocessed Esters and Fatty Acids (HEFA) at up to 100%. These tables align ISO 8217 with the FuelEU Maritime regulation’s trajectory toward biofuel blending and reflect operational experience with FAME and HVO blends.

Revised stability requirements. The TSP limits were adjusted to account for bio-blend effects on asphaltene stability. Bio-blends can stabilize or destabilize asphaltenes depending on the blend ratio and base fuel; the 2024 edition provides grade-specific guidance.

Annex A guidance. A normative annex was added on compatibility testing protocols for blended fuels, providing a step-by-step procedure that builds on ISO/PAS 23263:2019 experience.

Parameter alignment. Some parameter limits were tightened further in line with engine builder feedback accumulated between 2017 and 2024.

The 2024 edition is relevant to any ship bunkering from 2025 onward, as new supply contracts increasingly reference it. Ships should confirm which edition applies to each BDN, particularly for bio-blend purchases. The ISO 8217:2024 changes article covers the 2024 edition in more detail.

Limitations

Edition specification matters, and contracts lag updates. The 2024 edition changed several limits, but many existing bunker supply contracts still reference ISO 8217:2017 or even the 2010 edition. A parameter that meets the 2024 limit may fail the 2017 limit, or vice versa. Confirm the applicable edition before interpreting any certificate.

CCAI is a screening tool, not a substitute for ignition testing. CCAI was developed empirically for conventional HFO and residual blends. Its predictive value for VLSFO, particularly high-paraffinic VLSFO, is less well validated. Some VLSFOs with CCAI below 850 have exhibited poor ignition behavior; some with CCAI near 870 have burned cleanly. Engine bench testing per ISO 8178 is the gold standard for ignition quality assessment.

The 60 mg/kg cat fines delivery limit doesn’t protect the engine alone. The limit depends on the ship’s purification train reducing cat fines from 60 to below 15 mg/kg at the engine inlet. A purifier operating at incorrect temperature, with wrong gravity discs, or with insufficient residence time can fail to achieve this reduction. Regular cat fines monitoring at the purifier outlet is the only operational assurance.

ISO 8217 doesn’t cover all marine fuel contaminants. The standard targets known chemical contaminants measurable by the listed test methods. It doesn’t cover all possible chemical adulterants (chlorinated solvents, styrene, phenol, dicyclopentadiene). Several major contamination incidents, including the 2018 Houston contamination incident affecting dozens of ships, involved chemical contaminants not covered by any ISO 8217 parameter. Extended GC-MS (gas chromatography-mass spectrometry) screening is available from specialist laboratories but isn’t part of the standard.

MARPOL sampling is only as good as the sampler installation. The regulatory strength of the MARPOL sample depends entirely on the sampler being correctly installed, calibrated, and operated. Many older ships have non-compliant samplers (wrong installation point, grab-sample or drip-feed-by-hand substitutions) that would be challenged in dispute proceedings. Post-2020 PSC focus has increased scrutiny of sampling equipment during port state inspections.

The BDN density declaration is not a certified lab result. Suppliers typically determine BDN density from tank calibration tables or a quick hydrometer check at the terminal, not from ISO 12185. The density figure on the BDN is a commercial declaration, not an ISO/IEC 17025-certified measurement. Quantity disputes routinely center on density discrepancies of 3 to 8 kg/m3 between BDN and ship measurement.

See also

• Bunker Delivery Note: the MARPOL BDN document requirements and retention obligations
• MARPOL Annex VI Reg 18: Fuel Oil Quality: the regulatory BDN and sampling regime in detail
• MARPOL Annex VI Sulphur Cap: the global 0.50% cap and ECA 0.10% cap
• IMO 2020 Sulphur Cap: the 2020 implementation and VLSFO transition
• Emission Control Areas: ECA designations and the 0.10% sulphur requirement
• Heavy Fuel Oil: RMG 380 and residual fuel properties
• Marine Gas Oil: DMA/DMZ distillate grade properties and ECA use
• Marine Fuel Oil Systems: purification, heating, and cat fines management on board
• Marine Fuel and Lube Oil Purifiers: centrifugal separator operation and gravity disc selection
• FONAR and BDN Documentation: the FONAR procedure for non-availability
• ISO 8217:2024: the sixth edition changes in detail

Calculators:

• ISO 8217 Parameter Check: screen a lab certificate against ISO 8217 grade limits
• CCAI Calculator: compute CCAI from density and viscosity
• Bunker Density-Temperature Correction: VCF conversion per ASTM D1250/ISO 91-1
• Bunker Viscosity-Temperature: Walther equation for heater temperature
• Bunker Compatibility Spot: spot test screening for commingling
• Voyage Blend Compatibility: compatibility assessment for VLSFO blends
• ISO 14596 Sulphur by WDXRF: sulphur determination calculation
• ISO 12185 Density: oscillating U-tube density measurement
• ISO 3104 Kinematic Viscosity: viscometer calculation
• ISO 10370 Micro Carbon Residue: Micro CCR calculation
• ISO 10307-1 Total Sediment (Existent): TSP by hot filtration
• ISO 3733 Water Content: Karl Fischer water determination
• Bunker FONAR Sulphur: sulphur exposure quantification for FONAR filing
• Bunker Sampling Procedure: MARPOL sampling compliance check
• Flash Point Check: ISO 2719 flash point compliance