April 27, 2026 • 5 min read
De-fossilizing aviation: The structural case for SAF
Dr Geert Reyniers
Aviation won’t decarbonize by walking away from hydrocarbons, but by changing where they come from.
The debate around Sustainable Aviation Fuel (SAF) often centers around cost curves, technology readiness and policy support. But on a deeper level, it’s really a question of structural systems.
Aviation has always been restricted by physics. Long haul and widebody aircraft need very high gravimetric and volumetric energy density. Currently, no alternative energy carriers match liquid hydrocarbons on these dimensions.
That reality shapes every credible pathway forward. It means aviation will continue to rely on hydrocarbon molecules for the foreseeable future. What needs to change isn’t how jet fuel performs, but the origin of its carbon.
Continuing to rely on fossil-derived carbon is incompatible with long-term climate objectives. De-fossilization is structurally unavoidable, not optional.
De-fossilization is structurally unavoidable, not optional.
Systemic constraints on SAF scale up
SAF decouples hydrocarbon fuels from fossil resources. From a chemistry and thermodynamics point of view, this is a big step forward: fuel specification, infrastructure compatibility and engine performance only need moderate changes while switching the carbon source to biogenic or atmospheric. The core technologies already work. The challenge isn’t feasibility, it’s optimizing, scaling and integrating SAF into existing aviation systems.
Despite its technical feasibility, SAF deployment remains limited. And constraints are systemic, not singular. Compared to fossil jet fuel, SAF’s competitiveness is affected by a combination of factors. Feedstock availability, process efficiency, capital intensity and regulatory fragmentation all influence cost, risk and pace of deployment. But no single constraint can be solved in isolation.
Regulatory alignment will play a critical role in accelerating SAF uptake in the short- and medium-term. However, this article will focus on the structural constraints that sit beyond policy.
For mature pathways like Hydrotreated Esters and Fatty Acids (HEFA), the main challenge isn’t process chemistry. It’s feedstock scarcity. Lipid based feedstocks are finite and increasingly sought after by other sectors, placing a hard ceiling on potential growth.
More advanced pathways including Alcohol-to-Jet (AtJ) and e-fuels shift the constraint set. Here, the limiting factors are process maturity, scaleup risk and high energy input intensity. These pathways expand the feedstock pool, but introduce new challenges across capital deployment, infrastructure integration and system efficiency.
Efficiency gains and the de‑fossilization paradox
Aviation’s historical success improving aircraft and engine efficiency has reduced fuel burn per passenger kilometer. But while this helps slow overall emissions growth, it’s also lessened immediate pressures for alternative fuels by making small improvements seem sufficient for now.
From a systems perspective, this creates a paradox.
Efficiency improvements reduce demand growth but not the need for a non-fossil carbon source.
In the long term, efficiency and SAF address different parts of the emissions equation. That’s why they must be developed in parallel, not sequentially.
Technology evolution and the energy reality of SAF production
The SAF landscape is best understood as a portfolio of pathways, each at different stages of maturity, scalability and carbon circularity. HEFA has dominated early deployment because of its relative simplicity and compatibility with existing refinery infrastructure. But its reliance on finite lipid feedstocks limits its long-term contribution.
As demand increases, the industry is structurally driven toward ethanol‑to‑jet (ETJ) or methanol‑to‑jet (MTJ) pathways, which expand feedstock flexibility through alcohol intermediates and ultimately toward e‑fuels, where waste‑derived feedstocks are used to produce CO and CO2, becoming the carbon source itself. As an example, Power2x is progressing an eFuels Rotterdam project, for whom Worley has completed a FEL2 package and Class III Estimate.
This evolution reflects a broader shift.
The industry moves from partial lifecycle emission reduction towards true carbon circularity.
That point is achieved when atmospheric or biogenic CO2 is combined with renewable electricity to produce drop-in aviation fuels.
High specific energy consumption as a core limitation
Across today’s SAF pathways, one challenge that shows up consistently is high specific energy consumption. Most conversion routes rely on thermochemical processes like biomass gasification, reforming or Fischer‑Tropsch synthesis that operate at elevated temperatures and pressures. A fraction of that energy is then expended on driving the conversion process itself, rather than included in the final fuel product.
This energy intensity directly affects operating costs, lifecycle emissions, sensitivity to electricity and fuel prices and overall system efficiency. It’s not a marginal optimization issue; it’s a central determinant of SAF’s competitiveness and scalability.
Two complementary engineering directions
Addressing this challenge requires action in two technically distinct but complementary directions.
The first is decarbonizing energy input. Replacing fuel-based thermal energy with renewable electricity through advanced electrification, heat integration and system-level energy optimization across the SAF value chain. While this doesn’t necessarily reduce absolute energy demand, it can improve lifecycle emissions performance.
The second direction is more fundamental. It focuses on reducing the intrinsic energy intensity of conversion pathways themselves. Here, research is increasingly exploring biological and hybrid processes that operate at lower temperatures and pressures like enzymatic catalysis for biomass conversion and gas fermentation routes for alcohol production.
Enzymatic pathways as a medium-term innovation lever
Enzymatic routes to SAF or SAF precursors are still in early stage development. Their technical appeal lies in milder operating conditions, improved selectivity and potentially higher carbon efficiency. These characteristics offer a pathway to rebalance the energy economics of SAF production.
While not yet ready for large scale deployment, they represent an important component of the medium- to long-term innovation pipeline.
Ecosystem integration and the role of the system integrator
Building a viable SAF industry can’t be reduced to isolated technologies or projects. It’s a value chain optimization challenge. Success depends on alignment across feedstock supply, conversion technology, research, offtake structures, financing and policy frameworks.
Misalignment at any point can stall progress, even when individual components are technically sound.
An experienced advisory and project delivery partner can support developers to mitigate technical and commercial risks. And where risks can’t be eliminated, they help ensure those risks sit with the party best able to manage them.
Integrating the SAF ecosystem
Scaling SAF will depend on more than individual projects. It will take integration across policy, technology, capital and delivery. Lessons learned across first-of-a-kind facilities and technology scale up highlights where execution risks sit, and what can be done to reduce them.
Combining these insights with global project delivery capability and an international footprint creates the right conditions to align regulatory frameworks, investment models and industrial execution across regions and pathways. Helping move SAF from promising technology to investable, industrial reality.
