SAF Pathway Selection: HEFA vs ATJ vs FT vs PtL

Picking a sustainable aviation fuel pathway in 2026. Commercial reality check: HEFA dominates, PtL is the future, ATJ and FT are niche. Here's how to think about it.

The Landscape (as of 2026)

Global SAF production in 2026 is ~2 billion gallons, with ~85% from HEFA (hydroprocessed esters and fatty acids, using UCO/tallow/soy). FT-SPK biomass is <2%, ATJ is ~8%, and power-to-liquid (PtL / eFuels) is <1% but scaling fastest. The CORSIA baseline jet-A CI is 89 gCO2e/MJ; a pathway that doesn't hit <44 gCO2e/MJ doesn't earn meaningful credits.

If a project developer pitches you a new HEFA plant in 2026, the first question is where is the feedstock coming from? UCO is scarce, tallow is tight, and soy has an iLUC penalty that usually kills the CI benefit.

The Decision Matrix

Pathway	ASTM Annex	Blend cap	TRL	Capex ($/gal/yr)	Typical CI	Best when
HEFA	A2	50%	9	$4-7	13-55	Plentiful UCO/tallow/FOG feedstock; fast FID
ATJ (ethanol / isobutanol)	A5	50%	8	$6-10	11-65	Existing ethanol infrastructure; Midwest corn or cellulosic
FT-SPK (biomass/MSW)	A1/A4	50%	7	$9-14	5-15	Waste/biomass near hydrogen + power; MSW landfill avoidance credit
PtL / eFuel (CO2 + H2 → FT)	Pending (A8 eq.)	50%	7	$10-18	1-10	Abundant cheap renewable power + CO2; offtake contract in hand
HFS-SIP (farnesene)	A3	10%	8	$12-16	40-60	Niche — limited blend cap and feedstock
CHJ (catalytic hydrothermolysis)	A6	50%	7	$5-8	35-50	Triglyceride feed + single-step desire
e-SAF MeOH→Jet	Under review	-	6	$11-19	0-10	R&D / demo only in 2026

Why HEFA Still Wins Commercially

Lowest CapEx per gallon — it's essentially a vegetable oil hydrotreater with isomerization; Neste/HEFA units come in at $4-7/gal-yr vs $12-18 for PtL.
Highest TRL — 15+ years of commercial operation; banks finance it.
Feedstock flexibility — if UCO goes tight, you can run tallow, corn oil, PFAD, or soy (with CI penalty).
Fast ramp — plants can start up in 2-3 years from FID.

But: the feedstock bottleneck is real. Global UCO + tallow + other "waste fats" is ~10-12 million tons/yr. The aviation industry needs ~350 million tons of jet fuel. You cannot decarbonize aviation with HEFA alone.

Why PtL Will Dominate 2035+

CI approaches zero if you have renewable power (0-3 gCO2e/MJ achievable).
Feedstock is infinite — CO2 and water. No land-use or food competition.
Policy tailwind — EU ReFuelEU mandates 0.7% eSAF by 2030, 5% by 2040, 35% by 2050. US credits (45V, 45Q, 45Z) stack meaningfully.
Plant scale — Infinium's Reactive CO2 Capture process simplifies the RWGS/FT loop; HIF Global, Norsk e-Fuel also building.

But: cheap renewable power at <$20/MWh is required to compete. Capex is 2-3x HEFA. Hydrogen capex dominates — alkaline electrolyzer at $600/kW gets you close; PEM at $1,100/kW doesn't.

When to Pick ATJ

ATJ makes sense when:

You already own ethanol infrastructure (Midwest US, Brazil).
Cellulosic ethanol drops CI <20 (Miscanthus, corn stover).
Coproduct credit on ethanol CI (e.g., Gevo's regenerative ag program).

The LanzaJet Georgia plant (10 MMGPY) and Gevo Net-Zero 1 (55 MMGPY planned) are the benchmarks. Capex is higher than HEFA, but feedstock flexibility is better since you can pivot between corn and cellulosic ethanol with the same SAF unit.

When to Pick FT-SPK

FT-SPK makes sense when:

You have cheap biomass/MSW at the gate (landfill diversion credit is huge — CI drops to 5-10).
You have existing gasification experience (former IGCC, Sasol-adjacent).
Hydrogen is locally available or you can integrate steam methane reforming.

Fulcrum BioEnergy and Velocys are the models. Capex is punishing — gasifier + FT + hydrocracker + ASU is $9-14/gal-yr. Most projects stall at financing.

CI Hierarchy — Be Honest About What You're Buying

Pathway + feedstock	CI (gCO2e/MJ)	% Reduction vs jet-A
PtL with wind + DAC	1	99%
FT-SPK MSW (landfill avoidance)	5	94%
ATJ cellulosic ethanol	11	88%
HEFA UCO	14	84%
HEFA tallow	23	75%
ATJ sugarcane ethanol	24	73%
PtL grid + point-source CO2	44	51%
HEFA soybean oil (with iLUC)	54	39%
ATJ corn grain ethanol	66	26%

The Traps

Assuming all HEFA is CI 14. HEFA from soy with iLUC is CI 54, barely a reduction. Lock down feedstock before financing.
Building PtL without a power PPA <$30/MWh. You'll never be competitive.
Counting on 45V for 7-year horizon. The IRS GREET model calibration is still politically volatile; stress-test your economics at $1/kg-H2 subsidy.
Ignoring the certification cost — annex updates (PtL getting A8 status) are slow; don't count on it for FID justification.
Under-specifying the hydrogen balance. Every SAF process consumes H2; PtL needs 3-5x more than HEFA. Plan the electrolyzer capex honestly.

Bottom Line Recommendation Tree

Want commercial SAF in 2-3 years? → HEFA, with a locked UCO/tallow contract.
Have biomass/MSW and $15/gal-yr CapEx appetite? → FT-SPK with MSW feedstock (best CI).
Have renewable power <$30/MWh + CO2 source? → PtL is the play for 2030+. Infinium, HIF, NORSK models.
Sitting on ethanol infrastructure? → ATJ; cellulosic for meaningful CI.
Writing a 10-year corporate commitment? → Diversify: 40% HEFA, 40% PtL, 20% ATJ.

References

ASTM D7566-24a — Standard for Synthesized Jet Fuel Blends.
ICAO CORSIA Default Life Cycle Emissions Values (2024).
IEA (2023). Sustainable Aviation Fuels: Status & Outlook.
CARB LCFS Pathway Lookup Table (2024 update).
IRENA (2021). Reaching Zero with Renewables: Aviation.
Infinium Electrofuels Technical Brief (2024).
EU ReFuelEU Aviation Regulation (2023/2405).