Biofuels are fuels produced from organic materials rather than petroleum. They come in liquid and gaseous forms, ranging from the corn-based ethanol blended into most gasoline sold in the United States to experimental fuels made from genetically engineered algae. The field is typically organized into four generations, each defined by what it’s made from and how it’s produced.
Bioethanol: The Most Common Biofuel
Bioethanol is the highest-volume biofuel in the world. It’s produced by fermenting sugars or starches from crops, the same basic process used to make beer or wine, just scaled up enormously. In the U.S., corn accounts for over 95% of bioethanol production, with smaller amounts coming from barley, wheat, and beverage residues. In South America, sugarcane is the dominant feedstock, while Europe relies more on wheat and sugar beet.
Other sugar-rich and starchy crops used for ethanol include sweet sorghum, cassava, potato, sweet potato, and molasses. The yield varies by crop and process. Corn in a dry-grind facility produces roughly 0.32 liters of ethanol per kilogram of grain. Sugarcane-based ethanol, common in Brazil, benefits from a simpler conversion since the sugars don’t need to be broken down from starch first.
Biodiesel and Renewable Diesel
Biodiesel is made from fats and oils through a chemical reaction called transesterification. About 100 pounds of oil or fat is combined with 10 pounds of a short-chain alcohol to produce 100 pounds of biodiesel and 10 pounds of glycerin as a byproduct. The most common feedstocks are rapeseed oil (dominant in Europe), soybean oil (the Americas), and palm oil (Asia). Used cooking oil, yellow grease, and animal fats also work and are increasingly popular because they don’t compete with the food supply.
Renewable diesel is a related but distinct product. While biodiesel is chemically different from petroleum diesel, renewable diesel is processed to be chemically identical to its fossil counterpart. Both can be made from the same feedstocks, including camelina oil and rapeseed oil, which the EPA classifies as achieving around a 50% reduction in lifecycle greenhouse gas emissions compared to petroleum fuels.
Cellulosic Ethanol From Non-Food Biomass
Second-generation biofuels solve a core problem with first-generation ones: they don’t use food crops. Instead, they’re made from the tough, fibrous parts of plants, things like corn stalks left over after harvest, wheat bran, wood chips, and dedicated energy grasses like switchgrass and miscanthus.
The challenge is that the cellulose locked inside these materials is much harder to break down into fermentable sugars. Pretreatment methods like steam explosion, acid treatment, and specialized chemical processes are needed to crack open the plant fibers before fermentation can begin. The U.S. alone could sustainably produce about 370 million dry tons of woody biomass per year for this purpose, accounting for roughly 30% of the total biomass projected to be available for biofuel.
The payoff is significant. Cellulosic biofuels from feedstocks like switchgrass, energy cane, and corn stalks achieve at least a 60% reduction in lifecycle greenhouse gas emissions compared to gasoline. That’s substantially better than the 20% reduction typical of conventional corn starch ethanol.
Biobutanol: A Higher-Energy Alternative
Biobutanol is produced through fermentation, similar to ethanol, but offers better fuel properties. Its energy density is about 29 MJ per liter, compared to 25 MJ per liter for ethanol. That means a tank of butanol takes you further. It also mixes more easily with gasoline, doesn’t absorb water the way ethanol does, and can be used in standard gasoline engines without modification. These advantages make it a promising drop-in replacement, though production costs remain higher than ethanol for now.
Biogas and Biomethane
Not all biofuels are liquids. Biogas is a renewable gas produced when microorganisms break down organic matter in the absence of oxygen, a process called anaerobic digestion. Common feedstocks include dairy manure, food waste, municipal solid waste, and material captured from landfills.
Raw biogas is a mixture of methane and carbon dioxide. The methane content typically ranges from about 50% to 70%, depending on the feedstock. Dairy waste digesters and food waste facilities tend to produce biogas on the higher end of that range. When biogas is purified to remove carbon dioxide and contaminants, the resulting biomethane is chemically identical to natural gas and can be injected directly into gas pipelines or used to fuel vehicles designed to run on compressed natural gas.
Algae-Based Biofuels
Third-generation biofuels come from microalgae and cyanobacteria, microscopic organisms that naturally produce oils and alcohols. Algae can grow in saltwater, wastewater, or on non-arable land, so they don’t compete with food crops or fresh water supplies the way corn or soy do. They also grow far faster than terrestrial plants.
Extracting the useful oils from algae cells is the main technical hurdle. The cells have tough walls, and simply pressing them (the way you’d squeeze oil from soybeans) doesn’t work well. Instead, researchers use physical methods like ball milling and sonication to rupture the cell walls, followed by chemical solvents to pull out the lipids. Using methanol as a solvent combined with ball milling and microwave-assisted extraction, labs have recovered around 24% of lipids at moderate temperatures, with yields exceeding 70% at higher temperatures. These lipids can then be converted into biodiesel, renewable diesel, or jet fuel.
Sustainable Aviation Fuel
Aviation is one of the hardest sectors to decarbonize because planes need energy-dense liquid fuels. Sustainable aviation fuel (SAF) is a biofuel specifically engineered to work in jet engines. The most commercially mature type is HEFA, which stands for hydroprocessed esters and fatty acids. It’s made from the same oils and fats used for biodiesel (cooking oil, animal fat, plant oils) but processed differently to meet the strict specifications of jet fuel.
Other SAF pathways include alcohol-to-jet (converting ethanol or other alcohols into jet-range hydrocarbons), biomass gasification with Fischer-Tropsch synthesis (turning wood or crop waste into liquid fuel through heat and chemistry), and power-to-liquid (using renewable electricity and captured carbon dioxide). Current regulations limit how much SAF can be blended with conventional jet fuel, with maximum blending ratios varying by production pathway. HEFA is the most widely used today due to its technical maturity.
Fourth-Generation and Engineered Biofuels
The newest category uses genetic engineering to improve the organisms that produce biofuels. Scientists modify bacteria, yeast, and algae to increase their oil output, grow faster, or produce specific fuel molecules they wouldn’t naturally make. Genetically optimized cyanobacteria, for example, have been engineered to produce ethanol, butanol, isobutanol, and modified fatty acids directly from sunlight and carbon dioxide.
This approach blurs the line between biology and manufacturing. Rather than growing a crop, harvesting it, and converting it into fuel through multiple industrial steps, the engineered organism essentially becomes the factory itself. These fuels are still largely at the research and pilot stage, but they represent the direction the field is moving.
How Biofuel Production Breaks Down Globally
Biofuels currently supply about 5.6% of global liquid fuel demand for transportation. The IEA projects that figure will reach 6.4% by 2030, totaling around 215 billion liters per year. Production is concentrated in five regions: India, China, Brazil, the United States, and Europe, which together account for more than two-thirds of growth. Brazil and the U.S. dominate ethanol production, while Europe leads in biodiesel. Across all sectors (not just transport), renewable fuel demand reached 22 exajoules in 2023, which is about 5% of global energy demand for industry, buildings, and transport combined. That figure actually exceeds total global electricity generation from wind and solar PV.