Margin Shields: Feedstock Optionality in HEFA, AtJ, PtL Plants

The sustainable aviation fuel debate spends most of its energy on the wrong question. It asks which technology wins, HEFA, alcohol-to-jet, power-to-liquid, when the technologies all work and demand is already guaranteed by mandate. The question that actually decides who makes money is narrower and less discussed: which producer controls feedstock. Feedstock is 50 to 70% of the cost of SAF, and the supply of the cheap feedstock is capped. That makes SAF a feedstock-spread business, and it makes feedstock optionality the only durable margin shield.

Demand Is Guaranteed; Feedstock Is the Constraint

Start with what is not in doubt. The EU’s ReFuelEU Aviation mandate ramps blended SAF from 2% in 2025 to 6% by 2030 and 70% by 2050, with financial penalties for non-compliance, and the UK and others have followed. Demand, in other words, is legislated. That removes the question most clean-tech investors agonise over and replaces it with a harder one: where does the physical feedstock come from to meet a mandate that grows thirty-five-fold by 2050? SAF is not demand-constrained. It is feedstock-constrained, and the economics follow from that single fact.

The Cost Ladder, and Why Feedstock Dominates

Four pathways carry SAF today, and they sit on a clear cost ladder against fossil jet at roughly $850 a tonne.

Pathway	Feedstock	Cost $/t	Feedstock % of cost	Constraint
HEFA	Waste oils (UCO, tallow)	~$2,000	~60%	Capped supply, oil-linked
Alcohol-to-Jet (AtJ)	Ethanol (corn / cane / waste-gas / cellulosic)	~$2,400	~45%	Large, flexible
Gasification + Fischer-Tropsch	Biomass / MSW residues	~$2,450	~20%	Abundant, high capex
Power-to-Liquid (e-SAF)	CO2 + green hydrogen	~$4,800	~70% (power)	Unlimited, dearest

Two things jump out. First, in every pathway the input, not the converter, dominates the cost: feedstock or power is the majority of the stack. The clever reactor design is not where the margin is decided. Second, the cheapest pathway, HEFA, runs on the most constrained feedstock, while the most abundant feedstocks, biomass, municipal waste and CO2, carry the highest cost or capex. That tension is the whole investment problem in one table.

The HEFA Wall

HEFA is the cash cow of SAF today: commercially proven, lowest cost, and already deployed. But it runs on waste cooking oil and animal fats, and that supply is bounded by the food system, not by anyone’s ambition. Collection volumes grow slowly, and aviation competes for the same waste lipids as renewable diesel, which keeps UCO priced at $900 to $1,200 a tonne and occasionally above $1,400. This is a structural ceiling, not a cyclical one.

Put the legislated demand curve next to the waste-oil ceiling and the defining feature of the SAF market appears. The ceiling barely moves; demand explodes. By the 2030s the mandate outruns what HEFA can physically supply, and by 2050 the overwhelming majority of SAF, everything above the flat green line, has to come from somewhere else: alcohol-to-jet, gasification of biomass and municipal waste, and power-to-liquid. The HEFA wall is not a risk to be hedged. It is a dated, structural inflection, and it is the single most important thing to position around.

The Margin Shield: Feedstock Optionality

Because feedstock is the majority of cost and the binding constraint, the producer’s exposure to a feedstock price spike is the central risk, and the ability to avoid it is the central edge. We modelled a $300 per tonne feedstock spike against a $600 per tonne base margin.

A single-feedstock HEFA producer loses nearly two-thirds of its margin, falling to $225. A producer that can switch feedstocks absorbs far less, and a diversified portfolio across routes holds $465, barely flinching. That gap is the margin shield, and it has three distinct forms.

Shield one: feedstock flexibility

The clearest example is alcohol-to-jet. LanzaJet’s commercial Freedom Pines plant can run on corn ethanol, sugarcane ethanol, cellulosic ethanol, or ethanol made by fermenting industrial waste gases. When one ethanol source spikes, it moves to another. That optionality, not the conversion chemistry, is the asset. A HEFA plant hard-wired to waste oil has no such move; when UCO runs, its margin runs with it.

Shield two: co-product yield flex

A subtler shield sits inside the plant. HEFA and FT units co-produce renewable diesel and naphtha alongside jet, and the yield split can be tuned. When the SAF premium is rich, a producer runs in maximum-jet mode; when renewable diesel pays better, it shifts the slate. That flexibility to sell into whichever product carries the higher margin is a hedge most SAF commentary ignores, and it is a real, recurring source of resilience.

Shield three: oil-exposure diversification

This is where the macro of 2026 matters. SAF competes against fossil jet, which is oil-linked, so the recent crude spike lifted SAF’s competitiveness across the board. But the feedstock side is not uniform. HEFA’s waste-oil cost is itself partly oil-linked, because UCO competes with renewable diesel, whose value rises with crude, so a HEFA producer is squeezed from both ends when oil moves. PtL, by contrast, is power-linked, not oil-linked: its cost is driven by renewable electricity and CO2, not crude. A portfolio that spans oil-linked HEFA and power-linked PtL is therefore hedged against the very oil volatility the world has just been reminded exists. Optionality across feedstocks is, quietly, optionality across macro regimes.

The Other Half of the Feedstock Decision: Carbon Intensity

There is a second way feedstock decides margin, and it is the one most cost-focused analyses miss. The US 45Z credit and California’s LCFS do not pay a flat rate; they pay by lifecycle carbon intensity. The lower your fuel’s CI score, the more credit you earn per gallon. So the feedstock-and-process choice is not only a cost, it is a carbon score, and the carbon score is revenue.

Gevo, the listed alcohol-to-jet developer, has built its strategy around exactly this. Where LanzaJet’s edge is cost-side flexibility across ethanol sources, Gevo’s is carbon-intensity optimisation. It acquired Red Trail Energy’s low-carbon ethanol plant and its operating carbon-capture-and-sequestration site, roughly a million tonnes a year of sequestration capacity, specifically to drive the carbon score of its fuel down. Its planned ATJ-60 plant targets a carbon intensity of about −5 gCO2e/MJ, a negative score, by combining low-CI ethanol, renewable energy and CCS. Management has quantified the lever directly: a six to seven point reduction in CI is worth roughly an extra $0.10 a gallon in 45Z credits at its production scale. Stack enough CI reduction and the credit, not the SAF price, becomes a meaningful share of the margin.

That reframes the feedstock question once more. There are two ways to win it: flex feedstock cheaply, as LanzaJet does, or drive feedstock-and-process carbon intensity toward zero to harvest credits, as Gevo does, and the strongest positions do both. It also carries a caveat worth holding: these integrated, capture-heavy plays are capital-intensive and financing-sensitive, as Gevo’s 2026 withdrawal from a federal loan process for its first dedicated ATJ plant showed. The CI lever is real and valuable, but it is not free.

The Scale Future Is Already De-Risked

The reflex worry about the post-HEFA-wall pathways is that they are expensive and unproven at scale. Both are true, and both are being addressed by the same mandates that created the demand. ReFuelEU does not just mandate SAF in aggregate; it carries a dedicated synthetic-fuel sub-mandate that rises from 1.2% in 2030 to 35% by 2050. That is a legally guaranteed, price-insensitive demand floor for the most expensive and most scalable route, power-to-liquid, precisely the support an unproven pathway needs to attract capital. Meanwhile the feedstocks that can actually scale, biomass and municipal solid waste for gasification, and CO2 for PtL, are effectively unlimited and, in the case of MSW, come with a gate fee rather than a purchase price.

So the arc is legible. HEFA earns the cash today and hits its wall. AtJ, gasification and PtL inherit a demand curve that is legislated to grow, on feedstocks that do not run out, with a sub-mandate de-risking the hardest of them. The scale-up future of SAF is not a hope; it is a policy-backed transition from a constrained feedstock to abundant ones, and the value accrues to whoever owns optionality across that transition rather than betting the firm on the pathway that is cheapest this year.

How We’d Read the Opportunity

Do not underwrite a SAF producer on its technology; underwrite it on its feedstock position and its optionality. The durable winners are the players who can flex feedstock, who can shift their product slate, and whose portfolio spans the oil-linked present and the power-linked future. The HEFA pure-play is a cash-generative but terminal asset, to be valued as a high-return annuity with a hard end date, not a growth story. The scale value is in the optionality to ride the demand curve past the wall, on feedstocks the food system cannot cap. In a market where demand is guaranteed and feedstock is scarce, the margin shield is the moat.

What Clears an Investment Committee

1. A feedstock position, not just a plant. Contracted or owned feedstock with defined volume, price and contamination limits. Feedstock is the majority of cost; an uncontracted producer is a price-taker.

2. Demonstrated feedstock flexibility. Can the asset switch inputs, or is it hard-wired to one constrained stream? Optionality is the priced asset.

3. Co-product slate flexibility. Ability to flex the SAF, renewable diesel and naphtha split toward the best margin.

4. A view past the HEFA wall. If the thesis depends only on waste oil, it has a structural end date. Where does volume come from in the 2030s?

5. Macro-hedged exposure. Understand whether the cost base is oil-linked (HEFA) or power-linked (PtL), and size the portfolio so a crude swing does not break it.

SAF Feedstock: Investor FAQ

What is the biggest constraint on scaling SAF?

Feedstock, not demand or technology. Demand is guaranteed by mandates like ReFuelEU (6% by 2030, 70% by 2050). The cheap incumbent pathway, HEFA, runs on waste cooking oil and fats whose supply is structurally capped by the food system, which is the "HEFA wall." Scaling past it requires alcohol-to-jet, biomass and MSW gasification, and power-to-liquid.

How much of SAF cost is feedstock?

Typically 50 to 70% for HEFA, where used cooking oil runs $900 to $1,400 a tonne. Feedstock or power is the majority of the cost stack in every pathway, which is why SAF margin is a feedstock-spread game rather than a technology game.

What is the HEFA wall?

The structural ceiling on HEFA SAF set by the limited global supply of waste oils and fats, which is bounded by food-system volumes and contested with renewable diesel. Mandated SAF demand grows far faster than waste-oil supply, so by the 2030s most SAF must come from non-HEFA pathways.

Why is feedstock optionality a margin shield?

Because feedstock is the majority of cost, a producer locked to one feedstock loses most of its margin when that feedstock spikes; in our model a $300/t spike cuts a HEFA margin by nearly two-thirds. A producer that can switch feedstocks, flex its co-product slate, and span oil-linked and power-linked routes protects its margin. Optionality is the moat.

Does the high 2026 oil price help SAF?

Broadly yes, because SAF competes against oil-linked fossil jet. But HEFA feedstock is itself partly oil-linked (waste oils compete with renewable diesel), so a HEFA producer is squeezed on both sides, while power-to-liquid is oil-immune. A portfolio across both hedges crude volatility.

How does carbon intensity affect SAF margins?

Under credits like the US 45Z and California LCFS, payment scales with how low the fuel’s lifecycle carbon intensity is, so feedstock and process choices that lower CI raise credit revenue per gallon. Gevo, for example, estimates a six to seven point CI reduction is worth about $0.10 a gallon in 45Z credits, and targets a negative carbon score by pairing low-CI ethanol with carbon capture. The credit can become a meaningful share of margin, which makes carbon intensity a feedstock decision, not just an accounting one.

Methodology: SAF pathway costs on public 2026 ranges (HEFA ~$1,700-2,300/t; UCO 50-70% of cost; PtL ~$4,000-6,000/t near term). Margin-shield and HEFA-wall figures are illustrative, calibrated to disclosed feedstock prices and the ReFuelEU mandate trajectory; assumptions are Trident’s framework. Fossil jet ~$850/t at ~$87 Brent. Sources: IATA Global Feedstock Assessment to 2050; RMI; S&P; ScienceDirect HEFA review; ReFuelEU / Transport & Environment; Project SkyPower; Gevo Q1 2026 earnings & releases. Analysis, not investment advice.