What ISO 8217 covers
ISO 8217 is the international standard defining the minimum quality requirements for marine residual and distillate fuels. It specifies grade categories (RMA, RMB, RMD, RME, RMG, RMK for residual; DMA, DMB, DMZ, DFA etc. for distillate), quality parameters for each grade, and test methods. The current edition is ISO 8217:2024, though 2017 remains widely referenced.
Key residual grades explained
RMG 380 is the historical workhorse — maximum viscosity 380 cSt at 50°C. RMG 180 is lighter. RMK grades are higher density and viscosity. Post-IMO 2020, any of these can be specified at 0.50% or 3.50% maximum sulphur. VLSFO is typically RMG-range low-sulphur; HSFO is RMG-range high-sulphur.
Distillate grades explained
DMA is the standard marine gas oil — light distillate, no residual component, ≤1.50% sulphur in base spec. DMZ is similar. DMB is a distillate with limited residual content. For ECA compliance, 0.10% sulphur (LSMGO) specification is required and should be explicitly stated.
Critical quality parameters
Viscosity at 50°C (residual) or 40°C (distillate) — determines pumping, heating, and atomisation. Density at 15°C — affects injection and quantity conversion. Flash point — minimum 60°C (safety). Pour point — affects cold-flow behaviour. Water content — higher values indicate contamination. Sediment — mechanical/chemical filterable content. Cat fines (aluminium + silicon) — critical for two-stroke engine wear; 60 ppm max per ISO 8217 but many operators specify 40 ppm. CCAI (calculated carbon aromaticity index) — ignition quality indicator.
ISO 8217:2024 changes
The 7th edition was published on 30 May 2024 and is the most significant update in years. It restructures the standard from two tables into four: Table 1 distillate and bio-distillate fuels, Table 2 residual fuels at or below 0.50% sulphur, Table 3 bio-residual blends, and Table 4 residual fuels above 0.50% sulphur. New bio-distillate and bio-residual grades formally accommodate biofuel, with distillate grades permitting up to 100% FAME and new tests for FAME content, oxidation stability and cetane. It also caps organic chlorides at 50 mg/kg, adds a minimum viscosity for residual grades, and drops the winter/summer cloud-point split for distillates. Buyers should now specify explicitly that fuel is ordered to ISO 8217:2024, as the 2017 edition is still referenced in many commercial contracts during the transition. See also our guide to fuel stability, compatibility and cat fines.
Reading a bunker quality certificate
Key things to check: grade designation matches your order (e.g., RMG 380 VLSFO 0.50%), all parameters within spec, test lab accreditation (ISO 17025 is standard), and date of testing. Dispute any parameter out of spec or anomalous values. Third-party laboratory testing of retained samples is common for material disputes.
Frequently Asked Questions
Is 'off-spec' always material?
Not all off-spec results cause engine damage. Minor deviations in some parameters are operationally tolerable; others (cat fines high, water contamination, flash point low) are serious. Judgment and engine OEM guidance matter.
Can I order to a stricter spec than ISO 8217?
Yes. Many operators specify tighter cat fines limits (40 ppm rather than 60 ppm), specific viscosity bands, or additional parameters. Commercial contract terms govern; suppliers can usually accommodate reasonable tighter specs at cost.
What's the difference between the 2017 and 2024 editions?
2024 adds biofuel blend provisions and refines guidance on stability/compatibility. Most operational parameters are consistent across the editions. Your commercial contract should specify which edition applies.
Do I need to test every stem?
Third-party testing ('bunker quality analysis') is recommended for every material stem, particularly for VLSFO where blend variability is significant. Retained samples should be held per MARPOL requirements regardless.