Draft Figures — "The Specification Barrier: Why SAF Costs More Than Renewable Diesel"

Figure 1. California Renewable Fuel Volumes — RD vs SAF (2019–2024)

Annual volumes of renewable diesel and sustainable aviation fuel reported under California's Low Carbon Fuel Standard. RD volumes exceed SAF by two orders of magnitude despite shared feedstocks and similar production technology. Both fuels are predominantly HEFA-derived.
Million Gallons 0 500 1,000 1,500 2,000 2,500 3,000 3,500 480 1.9 2019 720 3.5 2020 1,176 8 2021 1,680 17 2022 2,400 36 2023 3,380 78 2024 Renewable Diesel Sustainable Aviation Fuel 253× 206× 147× 99× 67× 43×
Sources: CARB LCFS Quarterly Summaries (3Q2024); EIA renewable diesel production & consumption data; Stillwater Associates (2025). RD volumes are California consumption (EIA SEDS + CARB). SAF volumes from CARB LCFS opt-in reporting.

Figure 2. Environmental Attribute Value Stack — RD vs SAF in California (Feb 2025)

Comparison of total incentive value per gallon for renewable diesel and SAF at identical carbon intensity (40 gCO₂e/MJ) in the Los Angeles market. SAF receives $0.40/gal less in total incentive value, primarily due to exclusion from Cap at the Rack (CAR) and a lower RIN equivalence value.
$/gallon $0 $1 $2 $3 $4 $5 Spot ULSD $2.44 CAR $0.30 LCFS $0.42 D4 RINs $1.45 (1.7 EV) 45Z $0.17 $4.78 Renewable Diesel Spot Jet A $2.54 No CAR ($0.00) LCFS $0.41 D4 RINs $1.36 (1.6 EV) 45Z $0.17 $4.48 Sustainable Aviation Fuel −$0.40/gal Fossil spot Cap at Rack LCFS D4 RINs 45Z credit
Source: Stillwater Associates, "Tracking the Stacks" (Apr 2025), Feb 2025 average prices. CI = 40 gCO₂e/MJ. Los Angeles market. RD: 1.7 D4 RINs/gal; SAF: 1.6 D4 RINs/gal.

Figure 3. HEFA Product Yield Distribution — RD-Maximized vs SAF-Maximized Configuration

Product slate comparison for a HEFA plant processing identical lipid feedstock. Maximizing SAF yield requires additional hydrocracking, which shifts the product distribution toward lighter fractions (naphtha, LPG) that earn lower or no environmental credits. Net high-value fuel yield (RD + SAF) decreases from ~85% to ~70%.
RD-Maximized (HDO + Isomerization) Renewable Diesel — 83% 7% 5% ← Earns full RINs + LCFS + 45Z credits (83%) → Low/no credit value SAF-Maximized (HDO + Isom + Hydrocracking) SAF — 50% RD 20% Naphtha 15% LPG 8% 5% ← Full credits (70%) → Low/no credit value (30%) Net high-value yield loss: −13 percentage points + additional capital ($50–100M for hydrocracker) + higher H₂ consumption + catalyst costs Renewable diesel SAF (jet range) Naphtha LPG Fuel gas Water/losses
Sources: Lee Enterprises (Feb 2024); Baker & O'Brien (Nov 2024); Biotechnology for Biofuels (2017); ICAO SAF Rules of Thumb (Heyne/WSU). Yields are representative for soybean oil feedstock; actual yields vary by feedstock and catalyst configuration.

Figure 4. Specification Architecture — D975 (Diesel) vs D7566/D4054 (SAF)

Structural comparison of market entry requirements for renewable diesel vs. sustainable aviation fuel. RD faces a property-based specification with no process qualification and no blend limit. SAF faces a process-based qualification system with blend caps, multi-year testing, and additional property constraints that drive up production costs.
Renewable Diesel (D975) Property-based specification No process qualification required No blend limit — 100% drop-in Viscosity: 1.9–4.1 mm²/s at 40°C Cloud point: buyer negotiated No aromatics limit Standard diesel distribution Cost to enter market: ~$0 SAF (D7566 + D4054) Process-based qualification D4054: 5–7 years, $5–15M testing (4 tiers + OEM review + ASTM ballot) Blend limit: 10–50% maximum Viscosity: ≤8 mm²/s at −20°C + ≤12 mm²/s at −40°C Freeze point: ≤ −40°C (mandatory) Aromatics ≤ 25 vol% (blend) + Phosphorus ≤ 2 ppm Separate chain of custody until blended → re-identified as D1655 Cost to enter: $5–15M + years Same HEFA feedstock • Same lipid hydrotreating process • Same producer Yet fundamentally different market access, economics, and incentive eligibility
Sources: ASTM D975-24; ASTM D7566-24; ASTM D4054-22; DOE/BETO SAF Technical Pathways Review (2020). Qualification cost estimates from DOE and industry reports.

Figure 5. Timeline to Emissions Reduction by Decarbonization Pathway

Comparison of when each aviation decarbonization pathway begins delivering material CO₂ reductions. SAF specification reform applies immediately to the existing global fleet of ~25,000 aircraft. Non-drop-in alternatives require decades of aircraft development, fleet turnover, and infrastructure construction before meaningful impact. Shaded bars indicate the period from program launch to first material CO₂ reduction (>1% of sector emissions).
2025 2030 2035 2040 2045 2050 2055 SAF Spec Reform ~$50M SAF Policy Reform ~$0 (regulatory) New Engine (RISE) ~$5B+ Clean-Sheet Aircraft $15–32B Hydrogen Aircraft $700B–$1.7T Test 100% of existing fleet — immediate impact (25,000+ aircraft) Rule Fleet-wide impact — CAR inclusion, RIN parity Development + Certification Gradual fleet penetration Wider adoption Development + Certification (12 yr) Fleet turnover (15+ years) Aircraft dev + Infrastructure build (17+ yr) <15% of emissions addressable NOW Lighter bars = development/testing phase; Darker bars = operational emissions reduction phase
Sources: Airbus ZEROe timeline (Reuters, Feb 2025); CFM RISE target (2035+); Boeing 787/A350 development precedent; WEF/McKinsey infrastructure timeline; ASTM ballot process typical duration.