Marine Fuel Oil Grades: HSFO, MGO, IFO & VLSFO Compared

Marine fuel selection has become a precise engineering and compliance decision since the IMO 2020 sulphur cap reshaped global bunker markets. The regulation dropped the allowable sulphur content from 3.5% to 0.50% outside Emission Control Areas while ECAs maintain a 0.10% limit forcing operators to match fuel grades to trading routes and onboard equipment. This guide compares every major marine fuel oil grade from High Sulphur Fuel Oil (HSFO) and Intermediate Fuel Oil (IFO) through Very Low Sulphur Fuel Oil (VLSFO) and Ultra Low Sulphur Fuel Oil (ULSFO) to distillates including Marine Gas Oil (MGO), Marine Diesel Oil (MDO) and the ISO 8217 DMX, DMA and DMZ categories. You will learn the exact sulphur limits viscosity ranges density ceilings and handling requirements for each grade plus how ISO 8217:2024 updates introduce DF bio-blend grades and methanol specifications. The article details scrubber equivalence rules port discharge bans fuel changeover procedures for two-stroke and four-stroke engines and the practical stability testing needed before commingling VLSFO batches.

Marine Fuel Oil Grades at a Glance: HSFO, VLSFO, ULSFO, IFO, MGO, MDO, LNG

The IMO 2020 sulphur cap was a significant reduction from the previous global limit of 3.5% according to IMO. Today the market splits into residual fuels that require heating and distillates that do not. Residual grades include High Sulphur Fuel Oil (HSFO) with a 3.5% sulphur ceiling used only with scrubbers, Very Low Sulphur Fuel Oil (VLSFO) capped at 0.50% for global compliance, Ultra Low Sulphur Fuel Oil (ULSFO) at 0.10% for Emission Control Areas, and Intermediate Fuel Oil (IFO) 180 and 380 named for their kinematic viscosity at 50 °C. Distillate grades cover Marine Gas Oil (MGO) and Marine Diesel Oil (MDO) both limited to 0.10% sulphur plus the lighter DMX, DMA and DMZ categories defined by ISO 8217. Alternative fuels such as LNG, methanol and bio-blends are entering the bunker supply chain but remain niche compared to conventional oil grades.

Residual grades: HSFO, VLSFO, ULSFO, IFO 180/380

Residual grades HSFO, VLSFO, ULSFO and IFO 180/380 differ primarily in sulphur content and viscosity. According to IMO (before 2020), According to IMO (2020 onward), According to IMO (2020), IFO 180 and IFO 380 are legacy viscosity designations still quoted in many ports; IFO 380 roughly aligns with RMG 380 while IFO 180 aligns with RMG 180 under ISO 8217.

Distillate grades: MGO, MDO, DMX, DMA, DMZ

Distillate grades MGO, MDO, DMX, DMA and DMZ contain no residual component and therefore need no heating. According to IMO (2020), DMX is the lightest grade for emergency generators with a maximum viscosity of 5.5 cSt and a pour point below -30 °C. DMA is the standard marine distillate up to 6 cSt. DMZ permits a higher viscosity up to 6 cSt and a higher CCAI allowing slightly heavier blend components.

Alternative fuels snapshot: LNG, methanol, bio-blends

Alternative fuels snapshot LNG, methanol and bio-blends offer sulphur-free combustion but demand dedicated fuel systems. LNG requires cryogenic tanks at -162 °C and methane slip management. Methanol is liquid at ambient conditions but has a low flash point of 11 °C requiring double-walled piping. Bio-blends such as FAME or HVO dropped into VLSFO or MGO at up to 30% v/v under current ISO 8217:2024 DF grades reduce lifecycle CO2 but introduce cold flow and stability monitoring needs.

Grade	Sulphur Max %	Typical Viscosity	Density Max kg/m3	Primary Use
HSFO	3.50	180-380 cSt @50°C	991	Scrubber fitted vessels
VLSFO	0.50	10-380 cSt @50°C	991	Global compliance
ULSFO	0.10	10-380 cSt @50°C	991	ECA compliance
IFO 380	3.50	380 cSt @50°C	991	Legacy residual
IFO 180	3.50	180 cSt @50°C	991	Legacy residual
MGO	0.10	2-6 cSt @40°C	890	ECA / 4-stroke
MDO	0.10	2-11 cSt @40°C	900	4-stroke / auxiliary
DMX	0.10	1.4-5.5 cSt @40°C	890	Emergency generators
DMA	0.10	2-6 cSt @40°C	890	Standard distillate
DMZ	0.10	2-6 cSt @40°C	890	Higher CCAI distillate
LNG	0	N/A	450	Dual-fuel engines
Methanol	0	0.6 cSt @20°C	792	Dual-fuel engines

The table above summarises the key physical limits that drive bunker selection. Residual grades share a 991 kg/m3 density ceiling while distillates stay near 890 kg/m3 giving a clear separation in mass flow metering. Viscosity ranges dictate preheat temperatures: VLSFO at 380 cSt needs 130 °C at the injector versus MGO at 6 cSt needing none. According to IMO (before 2020), the 3.50% limit applies to scrubber-only HSFO. According to IMO (2020 onward), the 0.50% limit applies to global VLSFO. According to IMO (2020), the 0.10% limit applies to ECA grades ULSFO, MGO and MDO. Alternative fuels LNG and methanol show zero sulphur but vastly different densities affecting bunker tank sizing and energy content per voyage.

ISO 8217:2017 and 2024 Specification Tables: Residual (RM) vs Distillate (DM) Grades

ISO 8217 defines the mandatory quality envelope for every marine fuel delivered under a bunker delivery note. The 2017 edition established the RM residual and DM distillate families with limits on viscosity, density, CCAI, cat fines, flash point, pour point and FAME content. The 2024 edition adds DF distillate FAME grades, revises cold flow test methods and introduces methanol and DME specifications for dual-fuel readiness.

Residual RM grades RMA through RMK key limits

Residual RM grades RMA through RMK key limits step up in viscosity from RMA 10 at 10 cSt to RMK 700 at 700 cSt all measured at 50 °C. Density is capped at 991 kg/m3 for all grades. CCAI maximum rises from 850 for RMA to 870 for RMK indicating worsening ignition quality. Aluminium plus silicon (cat fines) is limited to 60 mg/kg for RMA through RMH and 80 mg/kg for RMK. Flash point minimum is 60 °C throughout. Pour point winter limits range from 0 °C for RMA to 30 °C for RMK. Total sediment aged must not exceed 0.10% m/m per IMO (2020). FAME is permitted up to 7.0% v/v in all RM grades under the 2017 standard.

Distillate DM grades DMA through DMZ key limits

Distillate DM grades DMA through DMZ key limits cover viscosity at 40 °C from 1.5 cSt for DMX up to 6.0 cSt for DMA, DMZ and DMB. Density maximum is 890 kg/m3 for DMX, DMA, DMZ and 900 kg/m3 for DMB. CCAI is not applied to distillates. Cat fines limit is 15 mg/kg for DMX and DMA and 30 mg/kg for DMZ and DMB. Flash point minimum is 43 °C for DMX and 60 °C for the others. Pour point winter limits are -30 °C for DMX, -6 °C for DMA and 0 °C for DMZ and DMB. Cloud point winter limits are -16 °C for DMX and -12 °C for DMA. FAME is limited to 7.0% v/v for DMA, DMZ, DMB and 0% for DMX in the 2017 edition.

ISO 8217:2024 updates: DF grades, revised cold flow, methanol/DME specs

ISO 8217:2024 updates DF grades, revised cold flow, methanol/DME specs to address biofuel blending and new fuel types. DF grades DMA, DMZ, DMB now allow up to 30% v/v FAME with mandatory oxidation stability and cold soak filtration tests. Cold flow properties replace pour point with Cold Filter Plugging Point (CFPP) for DF grades and introduce Winter Cloud Point for all DM grades. Methanol specification (DME grade) sets purity at 99.85% m/m, water at 0.1% m/m, ethanol at 0.1% m/m and chloride at 0.5 mg/kg per IMO (2020). DME grade requires 99.9% purity and similar contaminant limits. These additions enable bunkering of methanol and DME under the same quality framework as oil fuels.

Parameter	RMA 10	RMG 380	RMK 700	DMA	DMZ	DF-DMA
Viscosity cSt @50°C (RM) / @40°C (DM)	10	380	700	6	6	6
Density max kg/m3	991	991	991	890	890	890
CCAI max	850	870	870	-	-	-
Al+Si max mg/kg	60	60	80	15	30	15
Flash point min °C	60	60	60	60	60	60
Pour point winter max °C	0	30	30	-6	0	-6
FAME max % v/v	7	7	7	7	7	30

The specification table highlights the step changes between residual and distillate families. Viscosity jumps from 10 cSt at the light end of residual to 700 cSt at the heavy end while distillates stay at or below 6 cSt. Density separates cleanly at 991 kg/m3 for residual versus 890 kg/m3 for distillate. Cat fines allowance is four times higher in heavy residual (80 mg/kg) than in DMA (15 mg/kg) reflecting the refinery process streams. FAME limits show the 2024 DF-DMA grade opening the door to 30% v/v bio-blend versus 7% for conventional grades. Flash point remains a constant 60 °C minimum for all grades except DMX ensuring safe handling across the board.

IMO 2020 and ECA Compliance Map: Which Grade Where, Scrubber Equivalence

The IMO 2020 rule limits the sulphur in fuel oil used on board ships operating outside designated emission control areas to 0.50% m/m according to IMO (2020 onward). VLSFO and ULSFO meet this limit directly without aftertreatment. HSFO and IFO 380 or 180 only comply when the vessel operates an approved exhaust gas cleaning system. MGO and MDO are inherently compliant due to typical sulphur content well below 0.10%. The carriage ban prohibits holding non-compliant fuel oil above 0.50% sulphur on board unless the scrubber is fitted and operational. Port state control verifies compliance through bunker delivery notes and onboard fuel oil samples.

Emission control areas including the Baltic Sea, North Sea, North American coastal waters and US Caribbean Sea enforce a 0.10% m/m sulphur limit according to IMO (2020). Only ULSFO, MGO, MDO and LNG meet this threshold without abatement. VLSFO at 0.50% sulphur is non-compliant inside ECA boundaries unless a scrubber reduces equivalent emissions to 0.10% per IMO (2020). Vessels must complete fuel changeover before entry and after exit recording timestamps and volumes in the logbook. Boundaries are defined by coordinates in MARPOL Annex VI and local port regulations may impose stricter limits or require distillate only while at berth.

Scrubber open-loop, closed-loop, hybrid equivalence and port discharge bans

Open-loop scrubbers discharge washwater at sea and are restricted in ports such as Singapore, Fujairah, China coastal ports and several European harbours where discharge bans apply. Closed-loop systems recirculate washwater with caustic soda addition and retain sludge for shore disposal allowing operation in zero-discharge zones. Hybrid units switch between modes providing flexibility across regimes. Equivalence is certified under IMO Resolution MEPC.340(77) requiring continuous monitoring of pH, PAH and turbidity at the overboard outlet. Non-compliant washwater discharge leads to detention and fines under port state control regimes.

Grade	Sulphur Limit Met	Applicable Zone	Scrubber Required
HSFO / IFO 380	IMO global marine fuel sulphur cap	Global non-ECA	Yes
VLSFO	IMO global marine fuel sulphur cap	Global non-ECA	No
ULSFO	Sulphur limit in emission control areas	ECA and Global	No
MGO / MDO	Sulphur limit in emission control areas	ECA and Global	No
LNG	Sulphur limit in emission control areas	ECA and Global	No

The table maps each marine fuel grade to the sulphur limit it satisfies and the operating zone where it is compliant without aftertreatment. HSFO and IFO 380 only meet the global 0.50% cap when an approved scrubber is installed and operational per IMO (2020 onward). VLSFO meets the global cap directly but cannot be used in ECAs without a scrubber. ULSFO, MGO, MDO and LNG satisfy the stricter 0.10% ECA limit inherently per IMO (2020). Scrubber equivalence allows HSFO use in ECAs provided washwater discharge criteria are met and local port bans are observed.

Grade Deep-Dives: Properties, Handling, and Engine Suitability

HSFO and IFO: high viscosity heating, purifier settings, cylinder oil BN

HSFO and IFO 380 or 180 require storage at 50 to 70 degrees Celsius and heating to 130 to 140 degrees Celsius at the injector to achieve 10 to 15 cSt viscosity. Purifiers operate at 98 degrees Celsius with a gravity disc selected for 991 kg/m3 density feed. High cat fines up to 80 mg/kg demand two-stage centrifugal separation and fine filtration. Cylinder oil base number of 70 to 100 BN neutralises sulphuric acid from 3.5% sulphur combustion, per IMO limits before 2020. Two-stroke engines tolerate these grades with correct injection viscosity and cylinder lubrication matching fuel sulphur.

VLSFO and ULSFO: stability concerns, pour point range, lubricity

VLSFO and ULSFO blends vary widely in pour point from minus 6 to plus 30 degrees Celsius requiring tank heating capability even in tropical routes. Stability reserve is critical; incompatible blend components can precipitate asphaltenes clogging filters and purifiers. Spot testing with ASTM D4740 or D7060 is standard before commingling. Lubricity generally meets the 520 micron HFRR limit but low-viscosity ULSFO batches may need additives. Two-stroke engines require cylinder oil BN of 40 to 55 matching 0.50% sulphur fuel, per IMO limits from 2020 onward. Four-stroke engines accept these grades with standard materials.

MGO and MDO: cold flow properties, no heating needed, 4-stroke vs 2-stroke use

MGO and MDO remain fluid at minus 6 to minus 20 degrees Celsius pour point and need no heating system. Cloud point and CFPP dictate winter operability in polar routes. Viscosity at 40 degrees Celsius is 2 to 6 cSt allowing direct injection without viscosity control. Four-stroke medium-speed engines are the primary consumers. Two-stroke engines can burn distillates on low load but require pilot fuel or lubricity improvers to protect fuel pumps and injectors from low viscosity wear. FAME content up to 7% in DMA and 30% in DF-DMA demands compatible seals and frequent filter changes.

VLSFO vs HSFO: Technical Showdown on Viscosity, Stability, Combustion, and Emissions

Viscosity, density, CCAI, and cat fines limits comparison

VLSFO and HSFO diverge sharply on viscosity and density parameters that dictate purifier sizing and injection viscosity control. VLSFO grades under ISO 8217:2017 typically range from 10 to 380 cSt at 50 degrees Celsius while HSFO 380 sits at 380 cSt and HSFO 180 at 180 cSt. Density for VLSFO clusters between 900 and 975 kg/m3 versus 991 kg/m3 maximum for HSFO allowing marginally higher energy content per tonne for high sulphur fuel. CCAI values for VLSFO often exceed 850 indicating poorer ignition quality compared to HSFO averages near 830. Cat fines limits remain identical at 60 mg/kg for both RMG and RMK categories yet VLSFO blending streams frequently deliver higher actual loads requiring tighter purifier throughput. Within designated emission control areas the sulphur limit was already stricter at 0.10% according to IMO.

Parameter	VLSFO (RM Grade)	HSFO 380 (RMG)	HSFO 180 (RMK)	ISO 8217 Limit
Viscosity at 50°C (cSt)	10, 380	380	180	Max per grade
Density at 15°C (kg/m3)	900, 975	991 max	991 max	991 max
CCAI	850, 870 typical	820, 840 typical	820, 840 typical	870 max
Cat Fines (mg/kg)	60 max	60 max	60 max	60 max
Sulphur (% m/m)	0.50 max	3.50 max	3.50 max	Per grade

The table above highlights the operational envelope shift when switching from HSFO to VLSFO. Lower density reduces centrifugal separation efficiency requiring optimised bowl disc geometry and higher feed temperatures. Elevated CCAI demands earlier injection timing or pilot fuel strategies on two-stroke engines to maintain peak pressure margins. Cat fines parity on paper masks the reality that VLSFO cracking residues often carry finer particulate distributions that challenge standard 60 mg/kg compliance testing.

Stability testing: TSP vs shipboard spot test interpretation

Total sediment potential (TSP) under ISO 10307-2 remains the referee method for VLSFO stability reserve with a limit of 0.10% m/m per IMO (2020). Shipboard spot tests ASTM D4740 or D7060 provide rapid compatibility screening but cannot quantify absolute asphaltene precipitation risk. A TSP result below 0.05% generally indicates safe commingling while values approaching 0.10% mandate dedicated tank segregation per IMO (2020). Spot test ratings of 1 or 2 suggest compatibility yet false negatives occur when paraffinic VLSFO meets aromatic HSFO residues. Operators should retain representative samples for 12 months post-bunkering to support dispute resolution under the bunker delivery note clause.

Combustion differences: ignition delay, peak pressure, black carbon emissions

VLSFO exhibits longer ignition delay than HSFO due to lower aromaticity and higher paraffinic content shifting heat release later in the cycle. This reduces peak cylinder pressure by 2 to 4 bar on two-stroke engines at full load but increases exhaust gas temperature by 10 to 15 degrees Celsius. Black carbon emissions drop proportionally with sulphur reduction yet VLSFO aromatic fractions can produce higher particulate nucleation mode counts than HSFO at low loads. Cylinder oil base number must step down from BN 70-100 for HSFO to BN 40-55 for VLSFO to avoid deposit formation on piston crowns and liner walls. Four-stroke engines tolerate the transition with standard injection timing maps but require viscosity control at 13 to 17 cSt for mechanical fuel pumps.

Fuel Changeover Procedures: Step-by-Step for 2-Stroke and 4-Stroke Engines

2-stroke main engine changeover: HFO to VLSFO/MGO sequence

Two-stroke main engine changeover from HFO to VLSFO or MGO begins 12 hours before ECA entry by lowering fuel oil heater setpoints in 5 degree Celsius steps to reach 40 degrees Celsius for VLSFO or ambient for MGO. Purifier throughput increases to maximum rated capacity while fuel viscosity at injectors targets 13 to 17 cSt for VLSFO and 2 to 6 cSt for MGO. Cylinder oil BN switches from BN 70-100 to BN 40-55 at the 50% fuel viscosity crossover point with feed rate held constant for 24 hours then reduced by 15%. Scavenge drain monitoring intensifies to detect liner wash-down from lower viscosity fuel. Fuel pump lubrication relies on fuel viscosity; MGO changeover requires pilot fuel injection or lubricity additive dosing at 200 ppm to protect plungers and barrels.

4-stroke auxiliary engine changeover: HFO to VLSFO/MGO sequence

Four-stroke auxiliary engines complete changeover in 4 to 6 hours due to smaller fuel systems and lower thermal inertia. Viscosity controller setpoint ramps from 13 cSt to target 10 cSt for VLSFO or 4 cSt for MGO at 2 cSt per hour. Fuel pump cooling water temperature follows fuel temperature to maintain clearances. No cylinder oil BN change is required as trunk piston engines use system oil BN 30-40 throughout. Governor response is verified at 25%, 50%, and 75% load steps after fuel temperature stabilises. FAME content in distillate grades up to 7% in DMA requires seal compatibility confirmation and filter element change within 24 hours of switchover.

Cylinder oil BN selection and feed rate adjustment during transition

Cylinder oil base number selection follows fuel sulphur content not fuel grade. For 0.50% sulphur VLSFO the recommended BN is 40 to 55 with feed rate 0.6 to 0.8 g/kWh, per IMO (2020 onward). For 0.10% sulphur MGO in ECA the recommended BN is 25 to 40 with feed rate 0.5 to 0.7 g/kWh, per IMO (2020). During transition the feed rate remains at the higher HFO rate until drain oil BN analysis confirms alkalinity reserve above 15 BN. Over-lubrication with high BN oil on low sulphur fuel causes calcium carbonate deposits on piston crowns and ring grooves. Under-lubrication risks cold corrosion on liner walls when fuel sulphur drops below oil BN neutralisation capacity. Drain oil analysis every 500 running hours validates the feed rate strategy.

Step	2-Stroke Main Engine	4-Stroke Auxiliary Engine	Key Parameter	Safety Check
1. Pre-heat reduction	12 hrs prior 5°C steps	4 hrs prior 5°C steps	Heater outlet temp	Thermal shock avoidance
2. Purifier optimisation	Max throughput	Max throughput	Feed rate l/h	Bowl seal integrity
3. Viscosity target	13-17 cSt VLSFO 2-6 cSt MGO	10 cSt VLSFO 4 cSt MGO	Viscometer reading	Injection pump protection
4. Cylinder oil BN switch	At 50% viscosity crossover	Not required	BN 40-55 VLSFO BN 25-40 MGO	Drain oil BN >15
5. Load verification	25-50-75-100% steps	25-50-75% steps	Exhaust temp deviation	Governor stability

The changeover checklist above standardises the sequence for both engine types while highlighting critical divergences. Two-stroke engines demand cylinder oil management and fuel pump lubricity protection absent in four-stroke trunk piston designs. Viscosity ramp rates prevent thermal shock to fuel pump plungers and injector nozzles. Load verification steps confirm combustion stability before declaring the changeover complete. Port state control inspectors routinely request the changeover log with timestamps matching the bunker delivery note fuel grade declaration.

Bunkering Operations: BDN, Sampling, Quality Disputes, and Port State Control

BDN verification checklist: mandatory entries and red flags

The Bunker Delivery Note (BDN) must contain the supplier name and address, vessel name, port, date of delivery, product name, quantity in metric tonnes, density at 15°C, kinematic viscosity, sulfur content, and the MARPOL Annex VI Regulation 18.8.1 declaration signed by the supplier representative. Red flags include missing signatory details, viscosity or density values that fall outside the ordered ISO 8217 grade envelope, and handwritten corrections without countersignatures. The receiving chief engineer should cross-check the BDN quantity against the bunker surveyor’s sounding report before signing. Retain the original BDN onboard for three years as required by Regulation 18.9.1.

MARPOL Annex VI Reg 18.8.1 representative sample procedure

The MARPOL representative sample is drawn continuously throughout the delivery using a drip sampler installed at the manifold or a continuous flow sampler on the bunker barge line. The sampler must collect a minimum of 400 millilitres per 100 metric tonnes delivered with a total sample volume not less than 800 millilitres. The sample bottle is sealed with a tamper-proof label signed by both the supplier representative and the ship’s officer. One sealed bottle is retained onboard under the chief engineer’s custody for 12 months or until the fuel is substantially consumed. A second bottle is handed to the supplier for their retention. Port State Control officers verify the sampler calibration certificate and the unbroken seal chain during inspections.

Dispute timeline: lab analysis, supplier notification, arbitration clauses

When onboard testing or shore laboratory results indicate an off-specification delivery, the vessel must notify the supplier in writing within the timeframe stipulated in the bunker contract, typically 30 to 90 days from delivery. The notice references the BDN number, the specific parameter in dispute, and the test method used (usually ISO 8217 referenced methods). Most contracts refer disputes to arbitration in London, Singapore, or New York under LMAA, SIAC, or SMA rules. Preserve the MARPOL sample and the independent witness sample for joint analysis. If cat fines exceed engine maker limits but remain within ISO 8217 limits, the commercial argument centres on the "fit for purpose" warranty rather than the MARPOL sulfur compliance. Legal costs often exceed the fuel value so early settlement based on independent surveyor joint inspection is common.

BDN Field	MARPOL Requirement	Common Discrepancy	Action Threshold
Sulfur Content	Mass % per Reg 14	VLSFO declared 0.45% tests 0.52%	Exceeds IMO 2020 limit of 0.50% m/m
Kinematic Viscosity	cSt at 50°C (RM) / 40°C (DM)	RM grade declared 380 cSt tests 410 cSt	> Grade max limit
Density at 15°C	kg/m³	Declared 975 kg/m³ actual 992 kg/m³	> 10 kg/m³ variance
Cat Fines (Al+Si)	mg/kg (ISO 8217 max)	Declared 25 mg/kg tests 55 mg/kg	> 60 mg/kg (ISO) / > 15 mg/kg (Engine)
Pour Point	°C (Winter/Summer)	Declared -6°C actual +3°C	> Unheated tank temp

The table above maps the five most contested BDN parameters against their MARPOL or ISO 8217 regulatory anchors and the practical thresholds that trigger commercial disputes. Sulfur content remains the primary Port State Control focus because it determines regulatory compliance under the IMO 2020 rule effective from 2020 onward. Viscosity and density variances directly affect purifier throughput and quantity calculations. Cat fines disputes arise most frequently when engine maker limits of 15 mg/kg are breached despite the fuel meeting the ISO 8217 ceiling of 60 mg/kg. Pour point failures typically surface during cold weather voyages when unheated settling tanks approach the fuel’s solidification temperature.

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Conclusion

Match every bunker purchase to the vessel's trading pattern and installed equipment: VLSFO for global routes without scrubbers, ULSFO or distillates for ECA transits, and HSFO only when a class-approved exhaust gas cleaning system is operational. Verify each delivery against the bunker delivery note and ISO 8217:2024 limits for viscosity, density, cat fines and FAME content, and run a spot compatibility test before commingling any VLSFO parcels. Plan changeovers with the 12-hour stepped temperature reduction for two-stroke engines and the cylinder oil BN switch at the 50% viscosity crossover to avoid liner wear.

Confirm scrubber mode restrictions for every port on the voyage plan because open-loop discharge bans in Singapore, Fujairah and Chinese coastal waters force closed-loop or hybrid operation. Use Global Trade Plaza to compare verified supplier offers and bunker delivery note terms side by side, then cross-check counterparties through customs shipment records before committing to a stem.

Related reading: D6 Virgin Fuel Oil Specifications: Quality Data Sheet.

Frequently Asked Questions

what is marine fuel oil

Marine fuel oil is any petroleum product burned aboard ships for propulsion or power generation. It spans heavy residual grades requiring heating and lighter distillates that do not, each defined by sulphur content, viscosity and density limits under ISO 8217.

what is marine gas oil

Marine gas oil (MGO) is a distillate fuel with a maximum sulphur content of 0.10% and viscosity of 2 to 6 cSt at 40 °C. It contains no residual component, needs no heating and meets Emission Control Area limits directly.

what is marine diesel oil

Marine diesel oil (MDO) is a distillate grade also capped at 0.10% sulphur but may include a heavy cycle oil cutter stock raising viscosity up to 11 cSt at 40 °C. It is used in medium-speed four-stroke engines and auxiliary machinery.

what is bunker fuel oil

Bunker fuel oil is the commercial term for any fuel delivered to a ship's bunker tanks, covering residual grades such as HSFO, VLSFO and ULSFO plus distillates like MGO and MDO. The name reflects storage in bunkers rather than a single specification.

what is marine gas oil used for

MGO powers main engines, auxiliary generators and boilers on vessels operating inside Emission Control Areas or on ships without scrubbers. Its low viscosity and sulphur make it suitable for four-stroke engines and cold-start emergency generators.

how is marine gas oil made

MGO is produced by atmospheric distillation of crude oil, drawing the middle distillate cut between kerosene and light fuel oil. It undergoes hydrotreating to reduce sulphur below 0.10% and typically receives no residual blending.

what does marine gas oil look like

MGO appears as a clear, bright liquid ranging from pale yellow to light amber. It is free of water and sediment at delivery and has a density near 890 kg/m³, distinctly lighter than residual fuels.

marine fuel oil specifications

ISO 8217 defines mandatory limits for viscosity, density, CCAI, cat fines, flash point, pour point and FAME content. Residual RM grades share a 991 kg/m³ density ceiling; distillate DM grades stay near 890 kg/m³ with stricter cat fines limits.

marine gas oil specs

Under ISO 8217 DMA grade, MGO shows 2 to 6 cSt viscosity at 40 °C, density maximum 890 kg/m³, flash point minimum 60 °C, pour point winter -6 °C and FAME limited to 7% v/v (30% for DF-DMA).

marine diesel oil specifications

MDO aligns with ISO 8217 DMB or DMZ grades allowing viscosity up to 11 cSt at 40 °C, density maximum 900 kg/m³, flash point minimum 60 °C and cat fines up to 30 mg/kg. Sulphur remains capped at 0.10%.

bunker fuel oil specifications

Bunker delivery notes must reference ISO 8217 grade limits for the specific product supplied. Residual grades require viscosity 10 to 700 cSt at 50 °C, density ≤ 991 kg/m³, CCAI ≤ 870 and total sediment aged ≤ 0.10% m/m.

marine fuel oil price per metric ton

Price varies daily by port, grade and crude benchmark; VLSFO typically trades at a premium to HSFO while MGO carries the highest cost per tonne among conventional oils. Buyers compare Platts or Argus assessments against delivered bunker quotes.

Sources

• IMO (2020 onward): IMO global marine fuel sulphur cap