Diesel sulphur limits: which one applies to your market

In a diesel purchase contract, sulphur content takes up two characters and a unit. It is nonetheless the line that decides whether a cargo can legally be discharged, resold and used in the country of destination. A 500 ppm parcel is perfectly acceptable in some markets and refused in others, with nothing to tell the two products apart by eye.

Sulphur is not traded as a higher or lower quality. It is traded as compliance with a specific market, on a specific date.

What the figure actually means

Sulphur content is expressed in parts per million by mass, written ppm or mg/kg. The two units are strictly equivalent: 50 ppm means 50 milligrams of sulphur per kilogram of product, or 0.005 % by mass.

Beware of a frequent confusion in offers: some documents still express sulphur as a mass percentage, particularly for heavy products. A fuel oil at 0.50 % corresponds to 5,000 ppm. Reading "0.5" without checking the unit leads to comparing a product at 5,000 ppm with a product at 0.5 ppm, a factor of ten thousand.

This sulphur is neither an additive nor an accidental contaminant. It is present in the original crude oil, and the refinery removes it through hydrodesulphurisation, a process that consumes hydrogen, energy and time. The lower the target, the more expensive the treatment. That accounts for most of the price gap between grades.

Four worlds, four limits

There is no global standard. There are markets, each with its own threshold and timetable.

• European Union, EN 590: 10 ppm maximum, since 2009.
• United States, ULSD diesel: 15 ppm maximum, since 2010.
• East Africa, East African Community: 50 ppm, in force since 1 January 2015.
• West Africa, ECOWAS, imported products: 50 ppm, in force since 1 January 2021.
• ECOWAS local refineries: transitional regime, with a deadline set at 1 January 2025.

East Africa led the way. The June 2013 ministerial decision of the East African Community harmonised specifications at 50 ppm for diesel and 150 ppm for gasoline, gazetted in December 2013 for implementation on 1 January 2015.

West Africa followed seven years later. Meeting in Ouagadougou on 6 and 7 February 2020, ECOWAS environment and energy ministers adopted regional standards setting 50 ppm for imported fuels from 1 January 2021. Until then, some countries in the region admitted diesel at up to 10,000 ppm.

These thresholds sit within the AFRI specifications developed by the African Refiners and Distributors Association. AFRI-4 corresponds to 50 ppm for diesel and 150 ppm for gasoline; AFRI-5 targets the next step around 2030.

The dual regime trap

The point buyers most often miss comes down to one sentence: the limit applicable to imported product is not always the limit applicable to product refined locally.

ECOWAS explicitly created two regimes. Imported fuels had to meet 50 ppm from 2021, while refineries in the region were given additional time to upgrade their units. In Ghana, the regulator granted local refineries a waiver allowing them to produce diesel and gasoline at 1,500 ppm until December 2024.

The practical consequence for an importer: the product available on the domestic market may legally be far more sulphurous than what they are allowed to import. Taking the pump as a reference is a mistake. The only reference that counts is the regulation applicable to imports, in the country of destination, on the date of customs clearance.

What sulphur does to equipment

Three effects, of very unequal importance depending on the vehicle and equipment fleet.

• It poisons after-treatment systems. Particulate filters and nitrogen oxide reduction catalysts degrade irreversibly above a few tens of ppm. That is the technical reason behind the European 10 ppm threshold, not an abstract environmental requirement.
• It corrodes. Burning sulphur produces oxides which, combined with water, form acids. They attack tank walls and exhaust lines, and dilute engine oil. The effect is slow and cumulative.
• It emits fine particulates. This is the public health rationale that drove the successive African regulations.

A fleet made up mostly of older second-hand vehicles, without advanced after-treatment, tolerates a more sulphurous diesel without immediate damage. That explains why higher grades persist. But this mechanical tolerance says nothing about the legality of the import, and the two questions are regularly confused.

The test method matters as much as the figure

Here is the check almost nobody performs, and which sets an experienced buyer apart.

Two families of standardised methods measure sulphur:

• X-ray fluorescence (ASTM D4294, ISO 8754, ISO 20884), fast and inexpensive, perfectly suited to high contents.
• Ultraviolet fluorescence (ASTM D5453, ISO 20846), more precise, and the reference method at the low end of the range.

Around 10 ppm, X-ray fluorescence reaches the limits of its repeatability. A certificate stating "9 ppm by ASTM D4294" does not carry the same evidential weight as a result obtained by ASTM D5453.

For contract drafting: do not simply write a value, write the test method that must establish it. In a dispute between the loading laboratory and the receiving one, the contractual method settles the matter.

Five checks before signing

1. The regulation of the destination country, not domestic market practice, and its date of entry into force.
2. The unit used in the offer: ppm, mg/kg or mass percentage. Convert everything to ppm before any comparison.
3. The test method written into the contract, consistent with the target level.
4. Where and when the sample is drawn: is the governing value the one at the loading port, at the discharge port, or a contradictory average?
5. The margin between the stated value and the legal limit. A product declared at 49 ppm against a 50 ppm limit leaves no room for measurement uncertainty or residual tank contamination. Requiring a margin is ordinary prudence, not mistrust.

These five points belong to the documentary file that accompanies any serious cargo. They are verified on the certificate of quality and the inspection report, not on a commercial promise.

Key takeaways

• Sulphur content is a question of destination market, not of intrinsic quality.
• Thresholds move: 50 ppm in East Africa since 2015, in West Africa for imported product since 2021.
• Imports and local production do not always fall under the same regime. This is the costliest trap.
• A figure without a test method commits no one.
• A margin below the legal limit avoids a refusal to discharge.

Our diesel specifications are confirmed cargo by cargo, according to the destination market and the regulation that applies there. For a specific requirement, request a quotation.