Biodiesel (FAME): Techniques
One simple reaction, and the algae dream that stalled
What this tab covers The methods used to capture this energy: how each works, and how they compare on efficiency, cost, life-cycle emissions, maturity and scale.Two techniques are covered: making FAME biodiesel by transesterification of oils and fats, and growing algae as an oil source. Vegetable oils are projected to supply about 69% of bio-based diesel feedstock in 2035, and used cooking oil and tallow 23%.
Comparison
| Method | Efficiency | Cost | Life-cycle emissions | Maturity | Scale |
|---|---|---|---|---|---|
| Transesterification of vegetable oils (FAME)1245612 | About 100% mass yield; fossil energy ratio 5.54 for US soybean biodiesel | Representative Iowa soybean plant: capital USD 1.57 per gallon of annual capacity, 7.55 lb of soybean oil per gallon; average net return 2021-2026 was -USD 0.26 per gallon without tax credits and -USD 0.10 with them, so costs exceeded biodiesel prices | EU typical savings against 94 g CO2eq/MJ, excluding land-use change: rapeseed 52% (about 45 g CO2eq/MJ, calculated), soybean 55% (about 42), palm with methane capture 51% (about 46), palm with open effluent ponds 33% (about 63) | mature | US capacity 1,978 million gallons a year (September 2025); US output fell 40% from Q1 2024 to Q1 2025 as credit values fell |
| Transesterification of waste oils and animal fats147 | Mass yield similar to virgin oils | Not quantified | EU typical saving 88% for waste cooking oil (about 11 g CO2eq/MJ, calculated) and 84% for animal fats (about 15) | mature | Used cooking oil and tallow projected at about 23% of bio-based diesel feedstock in 2035 |
| Algae cultivation3 | Energy return 0.00092-0.35 (below 1) | Not quantified | Not quantified | research | No commercial fuel production identified |
The chemistry is cheap and well established; the feedstock decides cost and emissions. Waste cooking oil and tallow biodiesel save 84-88% of fossil diesel emissions under EU default values, while palm biodiesel from mills with open effluent ponds saves only 33% before land-use change, for which ICAO adds about 37 g CO2eq/MJ. Waste oils are limited, so most biodiesel still comes from food oils. Biodiesel increasingly competes with renewable diesel (HVO), which uses the same feedstocks but gives a fuel identical to fossil diesel. Algae remain a research topic because growing and processing them takes more energy than they yield.
How each method works
Transesterification of vegetable oils (FAME)Rapeseed, soybean or palm oil is mixed with methanol and a catalyst (usually sodium or potassium hydroxide). Each fat molecule splits into three methyl ester (biodiesel) molecules and one glycerin molecule, which settles out and is sold.1245612
Transesterification of waste oils and animal fatsThe same reaction is applied to used cooking oil or rendered animal fat, which are cheaper but more variable and need more cleaning first.147
Algae cultivationMicroalgae grow in ponds or closed tubes with sunlight, CO2 and nutrients. The cells are harvested, dewatered and their lipids extracted and converted to fuel; leftover biomass can be digested to methane.3
Sources
- Biodiesel Production and Distribution US Department of Energy, Alternative Fuels Data Center, 2025
- Energy life-cycle assessment of soybean biodiesel revisited (Pradhan et al., Transactions of the ASABE 54(3)) ASABE (abstract, University of Johannesburg repository), 2011
- The Energy Return on Investment for Algal Biocrude: Results for a Research Production Facility (Beal et al., BioEnergy Research) Springer (author copy, OurEnergyPolicy), 2011
- Directive (EU) 2018/2001 (Renewable Energy Directive II), Annex V: typical and default greenhouse gas savings for biofuels (Parts A and B); fossil comparator 94 g CO2eq/MJ. Default values not changed by amending Directive (EU) 2023/2413 (RED III); a Commission revision was in draft in 2026 European Union (EUR-Lex), 2018
- Monthly Biofuels Capacity and Feedstocks Update, Table 1: U.S. biofuels operable production capacity US Energy Information Administration, 2025
- Renewables 2025: Renewable transport International Energy Agency, 2025
- Food crops to remain backbone of global biofuel production through 2035 (summary of OECD-FAO Agricultural Outlook 2026-2035; feedstock shares are 2035 projections) Down To Earth, 2026
- Biodiesel Production Profits and Tax Credits (Irwin, farmdoc daily 16:46; representative Iowa soybean-oil FAME plant model) University of Illinois, farmdoc daily, 2026