What makes an aviation fuel sustainable?

LEARN SAF · By SAFV1 Editorial Team · Evidence reviewed 19 October 2026

Three questions need separate answers: can an aircraft use the fuel, what is its environmental performance, and does it qualify under the relevant programme?

The word “sustainable” can make a complicated assessment sound settled. A more useful starting point is to ask what claim is being made and which evidence supports it.

Technical suitability is the first question

A fuel must meet the applicable technical specification and conditions for use. Those requirements protect fuel quality and aircraft operation. They do not, by themselves, establish a lifecycle emissions saving or eligibility under a particular policy.

ICAO explicitly distinguishes conversion-process approval from the additional sustainability criteria needed for CORSIA. A technically qualified pathway can involve different inputs with different environmental outcomes.

Look across the fuel’s lifecycle

A lifecycle assessment counts emissions across the supply chain, rather than looking only at the aircraft exhaust. ICAO’s CORSIA methodology includes feedstock production or collection, processing, transport, conversion, distribution and combustion, with applicable land-use effects. Results are expressed in grams of carbon-dioxide equivalent per megajoule of energy, written gCO2e/MJ.

A lower carbon-intensity number represents fewer accounted emissions per unit of energy within that methodology. Comparisons need the same boundary and reference fuel. A percentage without those details is difficult to assess.

For illustration only, a hypothetical fuel at 30 gCO2e/MJ compared with a hypothetical reference at 90 would have a calculated saving of about 67%: (90 − 30) ÷ 90. These are teaching numbers, not a certified fuel result or programme threshold.

SAF still releases carbon dioxide when burned. Lifecycle savings describe the wider accounting comparison. They should not be reported as an equivalent reduction in the aircraft’s exhaust emissions.

The feedstock story needs records

Names such as “waste”, “residue” or “biomass” do not settle the assessment. A useful claim explains what the material is, where it came from and how those facts were verified. Ask what energy was used in processing and what assumptions were made about land use.

CORSIA eligible fuels must come from producers certified by an ICAO-approved sustainability certification scheme. Certification is a defined process with a scope, not a general endorsement of every product a company may sell.

Eligibility depends on the market

A fuel accepted for one purpose does not automatically qualify everywhere. The UK SAF Mandate guide, for example, excludes food, feed and energy crop-derived SAF and specifies its own minimum emissions-saving requirement. The EU’s ReFuelEU framework defines qualifying fuels through its own rules and the Renewable Energy Directive. Neither should be replaced by a generic statement that a pathway is “approved”.

Ask for the programme name, applicable version, certification scope and batch evidence. Then ask who is entitled to make which claim. Purchasing fuel, holding a compliance certificate and buying an environmental attribute are not interchangeable descriptions.

Read the claim before accepting the headline

Four details make an emissions claim more useful: the fuel and quantity covered; the comparison and calculation method; the evidence and verification; and the person or organisation entitled to use the resulting benefit. If a percentage concerns unblended fuel, it should not silently become a claim about the entire blended uplift or flight.

For the production routes behind these questions, start with What is SAF, and how is it made?

Sources and disclosure

Evidence reviewed 19 October 2026: ICAO conversion and lifecycle reference pages; CORSIA eligible-fuel documents listed through June 2026; UK DfT essential guide, published 19 December 2024; European Commission ReFuelEU overview. These explain distinct frameworks. This article does not certify a batch or determine a project’s eligibility.

SAFV1 was founded by CarbonCore, which publishes and currently supports the publication. Editorial responsibility rests with the SAFV1 Editorial Team. About SAFV1.