Biofuel Blend

A biofuel blend in aviation refers to a mixture of sustainable aviation fuel derived from biological or renewable non-fossil feedstocks and conventional petroleum-derived jet fuel, combined at approved ratios for use in commercial aircraft engines. The term is often used interchangeably with SAF blend, though biofuel blend emphasizes the biological origin of the renewable component — feedstocks such as used cooking oil, animal fats, agricultural residues, municipal solid waste, and energy crops — as distinct from e-fuels produced from renewable electricity and captured CO2. Biofuel blends are the most commercially ready form of low-carbon aviation fuel available today because they require no modification to existing aircraft, engines, or fuel distribution infrastructure.

What Is a Biofuel Blend?

Current ASTM D7566 standards allow biofuel blending at ratios up to 50 percent SAF with 50 percent conventional Jet-A or Jet-A1. This limit exists because SAF produced by most current commercial processes lacks certain aromatic hydrocarbon components that swell aircraft fuel system elastomers (seals and O-rings), maintaining seal integrity. At 50 percent blend, the conventional fuel's aromatic content provides sufficient swelling. Research is underway to qualify neat (100 percent) SAF for all operations, with several 100 percent SAF demonstration flights completed including Virgin Atlantic's November 2023 100 percent SAF transatlantic flight from London to New York. The blend composition is indistinguishable from conventional fuel to the aircraft — no sensor, fuel system, or engine modification is required, and pilots observe no performance difference in handling or fuel consumption.

How It Works in Practice

Biofuel blending occurs at fuel production facilities or fuel distribution terminals, where approved SAF is combined with conventional Jet-A in specified ratios and tested against ASTM fuel quality standards before delivery to airports. Airlines purchasing SAF typically do so through book-and-claim programs at hub airports, receiving blended fuel from commingled airport storage tanks rather than receiving physically segregated SAF. The book-and-claim model allows airlines to take credit for SAF volumes matching their purchases even if the actual molecules delivered to their aircraft are from a commingled tank. This accounting approach is necessary because physically tracking specific fuel molecules through aviation fuel supply chains is impractical. SAF certificates transfer ownership of the environmental attributes separately from the physical fuel, similar to renewable energy certificates in the electricity sector.

Why It Matters

Biofuel blends are the aviation industry's primary near-term decarbonization tool because they work within the existing aircraft fleet without modification. Long-haul widebody aircraft operating today will still be in service in 2040 to 2045, and they must reduce their carbon footprint using fuels rather than propulsion substitution. Government mandates are accelerating blend uptake: the EU's ReFuelEU Aviation regulation requires fuel suppliers at EU airports to blend a minimum of 2 percent SAF from 2025, rising through 6 percent in 2030, 20 percent in 2035, 34 percent in 2040, 42 percent in 2045, and 70 percent by 2050. The UK and other markets have implemented similar mandates. Meeting these targets requires enormous expansion of SAF production capacity, as global supply in 2024 was approximately 0.5 to 1 billion liters against a European mandate requirement of 4 to 5 billion liters by 2030.

Key Facts and Figures

• Maximum approved blend ratio under ASTM D7566: 50 percent SAF, 50 percent conventional Jet-A.
• Virgin Atlantic's November 2023 100 percent SAF transatlantic flight demonstrated neat SAF technical feasibility.
• EU ReFuelEU Aviation SAF blend mandates: 2 percent (2025), 6 percent (2030), 20 percent (2035), 70 percent (2050).
• Global SAF production in 2023: approximately 600 million liters (under 0.2 percent of total jet fuel demand of 350 billion liters or more).
• HEFA-SPK from used cooking oil, the dominant SAF type by volume, achieves 60 to 85 percent lifecycle CO2 reduction.
• Book-and-claim SAF accounting is accepted under CORSIA and most national regulatory frameworks.

Related Concepts

Sustainable Aviation Fuel, Carbon Intensity, Net-Zero Aviation, CORSIA, ETS Aviation