An alternative renewable fuel, produced from vegetable oils or animal fats through a refinery process called transesterification. Biodiesel contains no petroleum, but it can be blended at any level with petroleum diesel to create a biodiesel blend. Biodiesel is most commonly used as a blend of 20% biodiesel and 80% conventional diesel (called "B20"). Its use can result in substantial reduction of unburned hydrocarbons, carbon monoxide, and particulate matter. However, nitrogen oxide emissions tend to increase with biodiesel use. Provisions of the Energy Conservation Reauthorization Act (ECRA) of 1998 (P.L. 105-388) amended the Energy Policy Act (EPACT) of 1992 (P.L. 102-486) to allow that the use of biodiesel added to conventional diesel at blends of 20% and higher would produce credits to offset up to 50% each year of alternative fuel vehicle acquisition requirements. Farmers and processors anticipate that increased use of biodiesel will strengthen the market for soybean oil.