Co-processing is a refinery running bio feedstock through its existing units alongside crude oil. The renewable and fossil molecules come out inseparably mixed, so the renewable share is established by mass balance accounting rather than by physical segregation. For aviation this route is limited: ASTM D1655 Annex A1 permits co-processing at up to 5 %, well below the 50 % blending limit available to HEFA-SPK produced as a standalone fuel. The attraction is that co-processing needs no new plant, so it delivers renewable volume from existing refineries.
- 1Bio feedstock accepted at an existing unit
- 2Co-processed with fossil feed
- 3Renewable share determined by an approved method
- 4Allocated to the finished fuel
- 5Audited under the certification scheme
The molecules mix and cannot be told apart afterwards, so the renewable share is established by a testing or mass balance method the scheme approves, not by analysing the product. That method, not the chemistry, is what a buyer audits.
How it differs from a standalone renewable fuel
This distinction is worth getting right, because the two are frequently conflated in offers and they are not the same product.
- Standalone HVO or HEFA-SPK is made in a dedicated unit from bio feedstock only. The product is physically renewable throughout, and for aviation it blends into conventional jet at up to 50 % under ASTM D7566 Annex A2. See HVO and SAF.
- Co-processed fuel comes out of a conventional refinery that fed bio material in alongside crude. The molecules cannot be separated, so the renewable share is an accounting claim. For jet, co-processing is capped at 5 % under ASTM D1655 Annex A1.
- The commercial consequence: a co-processed barrel and a standalone barrel can both be genuinely renewable and still not be interchangeable, because the buyer's compliance framework may treat them differently.
Metallic octane boosters, and why they travel
Metal based octane improvers are a real and active trade, but almost none of it is European road fuel, and the reason is regulatory rather than technical.
| MMT (manganese) | Methylcyclopentadienyl manganese tricarbonyl. Effective anti knock, and it also protects valve seats in older engines on unleaded petrol. In the EU the Fuel Quality Directive caps it at 2 mg of manganese per litre, down from 6 mg in 2011. That cap binds long before the dose that would move octane usefully, which is why the volume goes to markets without the cap. |
|---|---|
| Ferrocene (iron) | Dicyclopentadienyl iron, CAS 102-54-5, an orange crystalline solid known as an octane improver since the 1950s. It also promotes smokeless combustion by catalysing soot oxidation, which is why it appears in burner and heavy fuel applications as well as petrol. Less studied than MMT, and several bodies advocate a precautionary approach to both. |
| The deposit question, for both | Metal in the fuel means metal in the engine. Manganese and iron both contribute to combustion chamber and exhaust deposits. Ferrocene oxidises to iron oxide and leaves a characteristic red deposit; at high dose it has been associated with valve stem wear. Dose discipline is not optional with these products. |
| Labelling | Fuel containing metallic additives has to be labelled as such under the EU rules. Worth knowing before you plan a blend for a European destination. |
Commercially this is why our octane booster business runs to West Africa, the Caucasus and similar markets rather than into the EU pool. We hold or can place stock close to those markets and we can move product by air when a blending window is closing. Customs classification matters here too: anti knock preparations sit under CN 3811 11 and 3811 19, apart from other additives under CN 3811 90, and getting that wrong stops a container.
What co-processing actually is, and why the accounting is the hard part
Co-processing means feeding renewable material into an existing oil refinery alongside fossil crude, rather than building a dedicated plant. The chemistry is the easy part. The accounting is where the deals are won and lost.
A refinery that puts, say, five per cent used cooking oil into its hydrotreater does not get a separate stream of renewable diesel out of the other end. It gets one blended product. The renewable share has to be attributed rather than measured, and how you are allowed to attribute it is a regulatory question with real money attached.
| Dedicated plant | Co-processing | Blending | |
|---|---|---|---|
| What happens | Feedstock converted in a purpose-built unit | Renewable feedstock fed into an existing refinery unit with fossil | Finished renewable fuel mixed with fossil fuel |
| Capital needed | High | Low. The unit already exists | None |
| Output | Physically separate renewable product | One blended product; renewable share attributed | Known blend of two finished fuels |
| The hard part | Financing and feedstock security | Proving the renewable share to a certifier | Logistics and specification |
| Method of proof | Mass balance, straightforward | Radiocarbon testing (ASTM D6866) or a yield model, depending on the scheme | Documentation |
ASTM D6866 is the physical check. It measures the biogenic carbon fraction using carbon-14: fossil carbon has none left, biogenic carbon does. That gives an independent measurement of the renewable share of a co-processed product, which is exactly what a sceptical buyer or auditor wants.
Why this matters commercially even if you never run a refinery: co-processing is the cheapest way for existing capacity to enter this market, and it competes for the same feedstock as the dedicated plants. When a large refiner starts co-processing, waste feedstock demand rises without any new plant being announced. That is a supply-side pressure most sellers do not see coming.
The products
- Co-processed kerosene, into aviation, subject to the 5 % limit and to whether the buyer's scheme recognises co-processed material for the claim it needs to make.
- Co-processed naphtha, into steam crackers as renewable petrochemical feedstock or into gasoline blending. This competes directly with bionaphtha, and the difference is in the accounting rather than in the hydrocarbon.
- Co-processed diesel and gasoline components, into road fuel pools under national renewable fuel obligations.
What has to be agreed
The recurring problem is a seller who can state the renewable percentage but not the method or the scheme behind it. In co-processed material the accounting is not supporting documentation, it is the product, and a buyer's compliance team will treat a missing method as a missing product.
| Renewable share | The percentage claimed, and the method used to establish it. |
|---|---|
| Mass balance method | Energy, mass or carbon basis, and the accounting period. |
| Certification scheme | ISCC EU, ISCC CORSIA, REDcert or RSB, with co-processing explicitly inside the certified scope. |
| Scheme recognition | Whether the buyer's specific framework accepts co-processed material for the claim being made. |
| Bio feedstock | What went in, and its Annex IX status. |
| GHG saving | The figure on the proof of sustainability for the renewable share. |
| Specification | ASTM D1655 for jet, with Annex A1 governing co-processing; the relevant road or petrochemical spec otherwise. |
| Destination treatment | How the national scheme in the delivery market counts it. |
How anyone proves a co-processed molecule is renewable
This is the awkward heart of co-processing. Once bio feedstock has gone through a refinery alongside fossil feed, the product coming out is molecularly identical to conventional fuel. You cannot separate the renewable molecules because in any meaningful sense there are none: there is one stream with a renewable share.
So the claim rests on two things working together, and both have to be sound or neither is.
- Mass balance accounting. The certified bookkeeping that tracks how much renewable feed went in and allocates a corresponding share of output. This is what a scheme audits. See ISCC certification.
- Radiocarbon verification. Biogenic carbon carries carbon-14; fossil carbon, being millions of years old, does not. Measuring the carbon-14 fraction tells you the biogenic share of a sample directly, whatever the paperwork says. ASTM D6866 is the standard method, with EN 16640 as the broader European framework and DIN 51637 written specifically for liquid fuels and blends.
The commercially important point: radiocarbon testing is the independent check on the mass balance. A refiner or an auditor can measure whether the renewable share you claim is actually in the barrel. If you are buying co-processed material, knowing that this test exists and can be run is worth more than any amount of assurance in an e-mail.
Frequently asked questions
How can anyone tell a co-processed fuel apart from fossil fuel?
Chemically you cannot, and that is the point: after co-processing the molecules are identical. What you can do is measure the biogenic share. Biogenic carbon contains carbon-14, fossil carbon does not, so a radiocarbon measurement gives the renewable fraction of a sample directly. ASTM D6866 is the standard method, with EN 16640 as the wider European framework and DIN 51637 aimed specifically at liquid fuels and blends. That measurement is the independent check on the mass balance paperwork.
Is a co-processed fuel worth the same as HVO?
Usually not, and treating them as interchangeable is a common and expensive error. HVO is a distinct product made in a dedicated unit and sold against EN 15940. A co-processed fuel is conventional fuel carrying a certified renewable share. They are accounted for differently, they price differently, and a buyer with a mandate to meet cares intensely about the difference.
What is co-processing?
A refinery running bio feedstock through its existing units alongside crude oil, so renewable and fossil molecules come out inseparably mixed. The renewable share is established by mass balance accounting rather than by physical segregation. Its attraction is that it produces renewable volume from existing plant without new investment.
What is the co-processing limit for jet fuel?
ASTM D1655 Annex A1 permits co-processing at up to 5 %. That is considerably lower than the 50 % blending limit available to HEFA-SPK produced as a standalone fuel under ASTM D7566 Annex A2, and it is the main technical constraint on the co-processed aviation route.
Is co-processed kerosene the same as SAF?
It is renewable aviation fuel, but it is not the same product as standalone HEFA-SPK and the two are not always interchangeable for compliance purposes. The limits differ, the accounting differs, and whether a buyer's framework recognises co-processed material for its specific claim has to be confirmed rather than assumed.
What is the difference between co-processed naphtha and bionaphtha?
Bionaphtha is the co-product of a dedicated hydrotreating unit running bio feedstock only. Co-processed naphtha comes from a conventional refinery that fed bio material in alongside crude, so its renewable share is a mass balance claim. Both can go to a steam cracker; which one a polymer producer can use depends on what its own customers require.
How is the renewable share verified?
Through mass balance accounting under a recognised voluntary scheme, with co-processing explicitly inside the certified scope. The method, whether energy, mass or carbon basis, and the accounting period both have to be stated. A renewable percentage without a stated method is not a usable claim.
Do all schemes accept co-processed fuel?
Not uniformly, and this is where deals fail. Recognition depends on the scheme and on the framework the buyer is claiming under. Establish what the end buyer actually needs to claim, and to whom, before agreeing anything else.
Market news
The most recent headlines touching this market, followed by wider news from across the feedstock and renewable fuel sector. The links go to the publisher; we do not host or edit their reporting, and a headline here is not our endorsement of it. Scroll for more.
- Kimchi waste could become viable feedstock for bioplastics
- Braskem biobased polymer helps Deterra drug disposal pouch earn packaging awards
- Eni and PETRONAS to explore high-performance bio-gasoline
- Linglong signs $2 billion Egypt investment MoU
- BTMA to represent European national associations at Tyres Europe board meetings
- Osaka Gas claims STS LNG bunkering first in Osaka Bay
- ISWG-GHG 22: Non-profits react
- USTC brings Copenhagen-based offices together in new hub
- ORLEN instigates new Baltic regional energy initiative
- TotalEnergies Lubmarine launches lubricant for 4-stroke medium speed marine engines
- IMO carbon price heads for December showdown
- LyondellBasell: Pyrolysis Reactors Installed for MoReTec Plant in Wesseling
- Sustainable aviation fuel pioneer completes successful trials
- Louis Dreyfus Company to generate biogas from citrus waste
- Nature by Design: A decade of IUCN, Monaco collaboration driving circular solutions for biodiversity
- European Digital Sustainability Skills Conference
- UCL reacts to IMO ISWG-GHG: ‘Steady progress on the Net Zero Framework’ made but ‘high uncertainty’ remains
- ISWG-GHG 22: ‘Genuine willingness’ for further NZF progress, observes Chair
18 headlines, updated automatically. Last refreshed .
Sources and further reading
Primary sources for the rules and figures on this page, so you can check them yourself. Legislation is amended: always read the consolidated text on the date that matters to you.
Who to ask about Co-processed naphtha & kerosene
Just ask. Co-processed volume to place or to source? Tell us the claim your buyer has to make and the scheme behind it. You get Bart van den Brug on the other end, same working day, in English or Dutch, and across the team also in French, Portuguese, Polish, Czech and Russian.
On how we work: on the feedstocks and fuels on this site we are a broker. We never take title, we do not trade our own book, and we are paid a commission on business that concludes. Additives are the one exception: those we also buy and sell for our own account, and we say in which capacity we are acting before you commit to anything. Either way you will hear it from us when the answer is no, or when your parcel is not ready for the conversation you want to have. A market read or a second opinion on a specification costs nothing and commits you to nothing.
Happy to look at whatever you have, even if it is half an analysis and a question.
+31 6 115 83 448
bart@sustainablecommodities.eu
Sustainable Commodities 3 B.V., Lemmer, the Netherlands
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Last reviewed 08 September 2026. Regulatory references are given for orientation and are not legal advice: verify against the current Official Journal text before contracting.