D6 virgin fuel oil: what it is, who really buys it, and the spec sheet red flags

D6 virgin fuel oil is one of the most searched and least understood products in the commodities market. The term appears in thousands of offers, nearly all for quantities and prices no refinery has ever shipped. This article explains what the grade is, who buys it, and how to recognise a fabricated specification sheet.

What D6 virgin fuel oil actually is

D6 is the informal name for Grade No. 6 fuel oil in ASTM D396, the US standard specification for fuel oils. It is the heaviest grade in that standard: a residual fuel left after atmospheric and vacuum distillation, often blended with cracked residues, that must be heated to be pumped and burned. In the US it is also called Bunker C or residual fuel oil. "Virgin" is not a term from the standard; it is a trade description meaning the product is straight-run refinery residue and has not been blended with used or re-refined oils.

ASTM D396 sets only a handful of limits for Grade No. 6, because it is a boiler fuel rather than an engine fuel:

• Flash point: minimum 60 °C (ASTM D93)
• Kinematic viscosity at 100 °C: 15.0 to 50.0 mm²/s (ASTM D445)
• Water and sediment: maximum 2.00 % v/v (ASTM D95 and D473)
• Sulphur: governed by the legal limit at the place of use, typically reported by ASTM D4294

Density, pour point, ash, vanadium and calorific value are not limited by the standard but are reported on a genuine certificate because the buyer's boiler or blending operation needs them. A real D6 certificate therefore has few hard limits and many reported values; a fake one tends to have the opposite.

Who really buys D6

Genuine demand for No. 6 fuel oil comes from a short list of users: power utilities with oil-fired steam plants, mainly in the Caribbean, Latin America, the Middle East and South Asia; refineries that buy residue as feedstock for coking or visbreaking units; bunker blenders who use it as a cutter component for marine fuels under ISO 8217; and some industrial boiler and asphalt operations. These buyers purchase on term contracts or tenders from refiners, majors and established trading houses, priced against Platts assessments for US Gulf Coast No. 6 at a stated sulphur content, and delivered by pipeline, barge or tanker under Incoterms 2020 terms such as FOB or CFR with inspection at loading.

None of these buyers accepts a "dip test" at a tank, pays for a "tank storage receipt", or issues a bank instrument before product has been inspected. Marine demand for high-sulphur residual fuel also fell sharply after the IMO 2020 sulphur cap, so the pool of buyers for 3 % sulphur D6 is smaller than the number of offers in circulation suggests.

Rule: D6 is sold by refineries to utilities and blenders under term contracts priced against Platts. An offer of D6 from a "mandate" with a discount to Platts, a dip test and a bank instrument before inspection is not a D6 offer. It is a document-fraud procedure with a product name attached.

Spec sheet red flags

The typical fake D6 sheet is copied from a template that has circulated for years. The following signs identify it:

1. Wrong standard cited. Sheets that list ASTM D1655, EN 590 or ISO 8217 methods for a product called D6 were assembled from other grades. D6 is ASTM D396.
2. Limits that do not exist. Lines such as "calorific value min 42 MJ/kg" or "pour point max 20 °C" presented as D396 limits do not appear in the standard.
3. Impossible combinations. A viscosity at 100 °C of 15 mm²/s with a density above 1,000 kg/m³ and a flash point of 150 °C does not describe a real residue.
4. Percent and ppm confusion. Sulphur stated as "max 2 %" on one line and "10 ppm" on another.
5. Units from the wrong market: gallons and API gravity for product allegedly in Rotterdam or Fujairah tanks, where residual fuel is sold per metric tonne.
6. No sample identity: no tank number, sample date, laboratory, report number or seal numbers. A sheet with "typical values" is not a certificate.
7. Volumes no refinery holds: 50 million gallons per month "available for 12 months" from a single tank farm.

Procedure red flags

The specification sheet is usually accompanied by a procedure that reveals the real intent. Common elements are a Tank Storage Receipt, an Authorisation to Verify, an injection report, a dip test fee, a request for a bank comfort letter or an MT799 before inspection, and a demand that the buyer issue a standby letter of credit under ISP98 or an MT760 against documents rather than against inspected product. A refinery sells against a letter of credit under UCP 600 payable against an independent certificate of quantity and quality issued at loading, and it has no need for any of these documents.

How a serious buyer proceeds

Any D6 offer that cannot pass this table without renegotiating the procedure should be closed as a file, not pursued as a deal.