Biodiesel is a renewable fuel made from vegetable oils, animal fats, or recycled cooking grease. Chemically, it is a methyl ester produced through transesterification. In plain terms, the oil is reacted with alcohol and a catalyst to make a fuel that burns like diesel but comes from plants or waste.

It can be blended with petroleum diesel at almost any ratio. B5 is 5 percent biodiesel. B20 is 20 percent. B100 is pure. Most modern diesel engines run on blends without modification. Older engines may need new hoses and seals because biodiesel can degrade certain rubbers.

The fuel has clear benefits. It cuts emissions of most pollutants and recycles waste grease. It also has limits. Feedstock supply is finite. Diverting food crops to fuel raises prices. Cold weather can thicken biodiesel, causing filter problems. Production scale remains small compared with petroleum diesel, though it fills a useful niche in fleets and farming.

Common feedstocks

• Soybean oil
• Rapeseed oil
• Used cooking oil
• Animal fats
• Palm oil