Fossil Diesel, Biodiesel, HVO & SAF: What's the Difference?
Not all diesel is created equal. As Australia moves toward lower-emission transport, fleet managers, sustainability teams, and procurement officers are increasingly encountering terms like "renewable diesel," "HVO," "biodiesel," and "SAF." These fuels can look identical in a tank but differ enormously in their chemistry, emissions profile, engine compatibility, and regulatory standing. Here is what you need to know.
Data note: All combustion emission figures cited in this article are drawn from the National Greenhouse Accounts (NGA) Factors 2025, published by the Australian Government Department of Climate Change, Energy, the Environment and Water (DCCEEW).
Fossil Diesel
The baseline: refined from crude oil
Fossil diesel has powered heavy transport for over a century. It is refined directly from crude oil and remains the dominant fuel for trucks, buses, mining equipment, and marine vessels worldwide.
Combustion emissions: ~2.7 kg CO₂-e per litre - the reference baseline against which all other fuels are measured. Its CO₂ is entirely fossil-derived, meaning every litre burned adds new carbon to the atmosphere.
Australian fuel standard: Fuel Quality Standards (Conventional Diesel) Determination 2025
International standard: EN 590 (Europe) / ASTM D975 (US) - specifies physical and chemical requirements for automotive diesel, including max 10 ppm sulphur (ULSD) and up to 7% FAME blending permitted.
More Information: Renewable Diesel vs Fossil Diesel: What It Means For Emissions In Australia
Biodiesel (FAME)
Plant and animal fats, chemically converted
Biodiesel, technically Fatty Acid Methyl Ester (FAME), is produced from biological feedstocks such as vegetable oils and animal fats through a chemical process called transesterification.
Combustion emissions: ~0.01 kg CO₂-e per litre (trace CH₄ and N₂O only). Under the NGA, its Scope 1 CO₂ combustion factor is zero - the carbon released was recently absorbed by living organisms (biogenic carbon), so it is not counted as a net addition to the atmosphere.
However, biodiesel has a different chemical structure to fossil diesel, which means blending limits apply and it is not approved for all engines. It can also affect performance in cold temperatures and has a shorter shelf life than fossil diesel.
Australian fuel standard: Fuel Quality Standards (Biodiesel) Determination 2025
International standard: EN 14214 (Europe) / ASTM D6751 (US) - specifies requirements for FAME biodiesel for use in diesel engines, including minimum 96.5% ester content. Blends up to B7 are covered by EN 590; B20/B30 captive fleet blends by EN 16709.
More Information: Renewable Diesel vs Biodiesel - How Are They Different?
Renewable Diesel (HVO)
Waste feedstocks, processed to diesel-identical chemistry
Hydrotreated Vegetable Oil (HVO), also called renewable diesel, is manufactured from 100% renewable waste feedstocks including used cooking oils, animal fats, and agricultural residues, through a hydrotreatment process.
Combustion emissions: ~0.01 kg CO₂-e per litre. Scope 1 CO₂ is zero under the NGA (biogenic carbon).
The result is a fuel that is chemically near-identical to fossil diesel, a direct drop-in replacement requiring no engine modifications, no blending limits, and no infrastructure changes. It carries full OEM approval across all major engine manufacturers. Across its full lifecycle, HVO delivers up to a 90% reduction in greenhouse gas emissionscompared to fossil diesel.
Australian fuel standard: Fuel Quality Standards (Paraffinic Diesel) Determination 2025
International standard: EN 15940 (Europe) - the dedicated standard for paraffinic diesel fuels from synthesis or hydrotreatment, covering HVO and GTL. Defines two classes (high cetane and normal cetane) and confirms compatibility as a drop-in for EN 590 engines with OEM approval. Also meets ASTM D975 (US diesel specification).
SAF (Sustainable Aviation Fuel)
Low-carbon fuel certified for jet aircraft engines
Sustainable Aviation Fuel (SAF) is produced using similar principles to HVO. It is a low-carbon aviation fuel produced from renewable sources like biogenic waste (used cooking oils, animal fats) or non-biogenic synthetic sources (green hydrogen and carbon dioxide). Biogenic SAF can reduce lifecycle carbon emissions by up to 80% compared to conventional jet fuel, whilst synthetic (non-biogenic) SAF, or e-fuels, can reduce these emissions by up to 90% (source: Qantas).
It is designed as a "drop-in" fuel, but currently is required to be blended with fossil jet fuel up to a 50% blend. SAF is not interchangeable with ground vehicle diesel - it is an entirely separate fuel category for jet aircraft only.
In Australia, there is currently no dedicated domestic fuel quality standard for SAF. It is certified under international aviation standards (ASTM D7566/D1655). Australia is actively consulting on SAF mandates and domestic standards, but none have been introduced at the time of writing.
Australian fuel standard: No dedicated Australian fuel quality standard yet.
International standard: ASTM D7566 governs neat SAF production and defines approved production pathways and maximum blend ratios (typically up to 50% with conventional jet fuel). Once blended, SAF is re-certified under ASTM D1655 - the global standard for conventional aviation turbine fuel (Jet A/A-1) - making it a full drop-in for existing aircraft and infrastructure. Currently 11 ASTM-approved production pathways exist, with HEFA (the same hydrotreatment process used for HVO) being the most common.
Side-by-Side Comparison
| Feature | Fossil Diesel | Biodiesel (FAME) | Renewable Diesel (HVO) | SAF |
|---|---|---|---|---|
| Feedstock | Crude oil | Vegetable oils, animal fats | Waste oils, animal fats, agricultural waste | Renewable / waste feedstocks |
| Production process | Refining | Transesterification | Hydrotreatment (HVO) | Hydrotreatment + aviation refining |
| Drop-in compatible | ✓ Baseline | ✗ Blending limits apply | ✓ Full drop-in, no modification needed | ✗ Aviation engines only |
| OEM approval | ✓ Universal | ~ Limited / blend-dependent | ✓ All major manufacturers | ✓ Aviation certified |
| Combustion CO₂-e (NGA 2024) | ~2.7 kg/litre | ~0.01 kg/litre | ~0.01 kg/litre | Recognised as renewable aviation kerosene |
| Scope 1 CO₂ (NGA) | Full fossil CO₂ | Zero (biogenic) | Zero (biogenic) | Reduced vs jet kerosene |
| Lifecycle GHG reduction | Baseline (0%) | Significant reduction | Up to 90% | Significant reduction |
| Cold weather performance | ✓ Good | ✗ Can gel / degrade | ✓ Equal to fossil diesel | N/A |
| Storage stability | ✓ Long shelf life | ✗ Shorter shelf life | ✓ Long shelf life | ✓ Standard aviation spec |
| Australian fuel standard | Conventional Diesel Determination 2025 | Biodiesel Determination 2025 | Paraffinic Diesel Determination 2025 | No domestic standard; ASTM D7566/D1655 |
| * Emission data based on National Greenhouse Accounts (NGA) Factors 2024. ✓ = Yes ✗ = No ~ = Partial/conditional | ||||
Key Considerations for Diesel Users
1. Scope 1 emissions reporting under NGER
Both biodiesel (FAME) and renewable diesel (HVO) carry a zero Scope 1 CO₂ combustion factor under the NGA Factors 2024. For organisations reporting under the National Greenhouse and Energy Reporting (NGER) scheme, this can significantly reduce reported direct emissions.
2. Engine and OEM compatibility
Renewable diesel (HVO) is the only low-carbon liquid fuel with unrestricted drop-in compatibility across all major engine manufacturers. Biodiesel blending limits vary by OEM and engine age, and high-blend FAME can void warranties. Always verify with your OEM before switching or contact us to seek clarification.
3. SAF is not a diesel substitute
SAF is purpose-built for jet turbine engines and meets an entirely different set of specifications. Ground fleet operators should disregard SAF as an alternative to diesel - it plays no role in road or off-road transport.
4. Lifecycle vs combustion emissions
The NGA figures reflect combustion (Scope 1) emissions only. Lifecycle analysis includes feedstock cultivation or collection, processing, and transport - and paints a fuller picture. HVO's up to 90% lifecycle reduction is an aggregate of all these stages, making it one of the strongest claims in the current market.
5. Regulatory landscape is evolving
Australia's renewable fuel standards and renewable fuels policies are constantly developing. The Paraffinic Diesel Determination 2025 formalises HVO's status. Federal and state government policy is advancing and already supports HVO as an immediate low carbon liquid fuel alternative that in some large emitting industries (such as Mining) will soon be mandated. Organisations planning multi-year procurement should monitor updates from DCCEEW and the Department of Infrastructure.
Disclaimer: This article is intended as a general information resource only. Emission factors are sourced from the National Greenhouse Accounts (NGA) Factors 2025 and reflect combustion emissions unless otherwise stated. Fuel quality standards referenced were current as of 2025. Engine and OEM compatibility should always be verified directly with the relevant manufacturer. This content does not constitute legal, regulatory, or technical advice.