Used cooking oil has become a surprisingly valuable commodity, fueling everything from diesel engines to jet planes to bars of soap. The global market for used cooking oil hit an estimated $8.56 billion in 2025 and is projected to double over the next decade. What was once just kitchen waste now sits at the center of a growing recycling economy, with uses that span energy, agriculture, manufacturing, and more.
Biodiesel: The Biggest Use
The single largest destination for used cooking oil is biodiesel production. The conversion process, called transesterification, is straightforward in principle: triglycerides in the oil react with an alcohol (usually methanol) in the presence of a catalyst. The mixture separates into two layers. The top layer is biodiesel; the bottom is glycerol, a byproduct used in cosmetics and pharmaceuticals. The biodiesel layer gets washed with hot water, filtered, and dried.
Under optimized conditions, this process can achieve a 93% yield, meaning almost all of the oil gets converted into usable fuel. The resulting biodiesel works in standard diesel engines, either on its own or blended with petroleum diesel. It burns cleaner, too. Life cycle analyses show that biodiesel made from used cooking oil produces roughly 5 to 7 grams of CO₂ per megajoule of energy, compared to 93 grams for conventional diesel. That translates to carbon emission savings between 81% and 89%.
Sustainable Aviation Fuel
Airlines are under growing pressure to cut emissions, and used cooking oil is one of their best options right now. Sustainable aviation fuel, or SAF, can be produced from used cooking oil through a process that converts the oil’s fatty acids into a fuel chemically similar to conventional jet fuel. SAF made this way can reduce lifecycle aviation emissions by up to 80%.
Countries are investing heavily in this. Egypt, for example, has announced plans for two SAF production facilities using used cooking oil as feedstock, with a combined capacity of 320,000 tons per year. Because batteries are too heavy for long-haul flight and hydrogen infrastructure doesn’t yet exist at scale, SAF from waste oils is the most practical path the aviation industry has for reducing its carbon footprint in the near term.
Soap and Cleaning Products
Turning fat into soap is one of the oldest chemical processes humans know, and used cooking oil works well for it. Researchers at the Fashion Institute of Technology published work showing that different types of waste cooking oils produce soaps with distinct properties. The thickness, transparency, and color of the final product all vary depending on whether the source oil was canola, soybean, or something else. Beyond traditional bar soap, used cooking oil can be processed into bio-based soft materials like gels for consumer cleaning products.
For home use, making soap from used cooking oil is a practical zero-waste project. The basic chemistry involves mixing the oil with lye (sodium hydroxide) and water, a process called saponification. The result is a functional, if rustic, cleaning soap.
Animal Feed
In many countries outside the European Union, recycled cooking oils are added to livestock feed as an energy-dense fat source. Oils recovered from industrial frying processes are mixed into chicken and rabbit feed at concentrations of 30 to 60 grams per kilogram. Research published in the Journal of the Science of Food and Agriculture found that adding recovered frying oils to animal feed had minimal effect on the fatty acid composition of the animals’ meat, liver, and plasma. Tissue oxidation levels also remained low.
One notable change: animals fed recovered oil had lower vitamin E levels in their tissues, reflecting the reduced vitamin E content of oil that has already been heated repeatedly. The European Union banned this practice as a precaution, but it remains common in other parts of the world where regulations differ.
Other Industrial Applications
Used cooking oil serves as a raw material for biolubricants, which are biodegradable alternatives to petroleum-based industrial lubricants. These are used in machinery, hydraulic systems, and metalworking where environmental contamination is a concern. The oil can also be processed into surfactants, the active cleaning agents in detergents and industrial degreasers. Some municipalities even use processed cooking oil as a dust suppressant on unpaved roads or as a release agent in concrete manufacturing.
Why Proper Disposal Matters
For every gallon of used cooking oil that gets recycled, there’s plenty more going down kitchen drains, where it causes real damage. When grease enters a sewer line, it solidifies and clings to the inside of pipes. Over time, small particles accumulate into massive blockages. These clogs can force raw sewage to back up onto private property or spill into waterways. Flushing grease with hot water only pushes the problem further downstream, where it hardens anyway.
Many cities have free collection programs to prevent this. San Diego, for instance, offers a year-round cooking oil recycling bin at its Miramar Landfill Recycling Center, accepting up to 30 gallons per visit at no charge. If you don’t have access to a collection program, the best approach for small amounts is to pour cooled oil into a non-recyclable container like a milk carton, let it solidify in the refrigerator, and toss it in the trash. For liquid oils that won’t harden, soaking them up with paper towels, newspaper, or cat litter before throwing them away keeps them out of your pipes.
A Growing Global Market
The used cooking oil market is projected to grow at 7.2% annually, reaching an estimated $17.18 billion by 2035. Several forces are driving this. Government mandates for renewable fuel blending create steady demand for biodiesel feedstock. Airlines committing to net-zero targets need SAF, and used cooking oil is one of the cheapest approved feedstocks. At the same time, collection infrastructure is expanding, with more restaurants and municipalities setting up recycling programs that channel oil into the supply chain rather than into landfills or sewers.
For restaurants, selling used cooking oil to recyclers has shifted from a disposal cost to a small revenue stream. For households, it’s worth checking whether your city offers free collection, since the oil you’d otherwise throw away has genuine economic and environmental value sitting in that fryer.