Biodiesel is mono-alkyl esters of long chain fatty acids derived from naturally occurring oils or fats which conform to ASTM D6751 specifications. Biodiesel refers to the pure fuel before blending with traditional distillate type petroleum-based fuels such as diesel fuel or home heating oil (petrodiesel). Biodiesel blends are denoted as, "BXX" with "XX" representing the percentage of biodiesel by volume contained in the blend (i.e.: B20 is 20% biodiesel, 80% petrodiesel). Biodiesel offers a near-term opportunity to displace petroleum-based heating oil with a low carbon, renewable fuel. Biodiesel can be made from a variety of domestically produced oils and fats such as commonly available vegetable oils or animal fats as well as other oils such as used frying oils, reclaimed distillers corn oil from ethanol plants, algal oils, etc. In the US, about half the biodiesel is made from soybean oil, with the remainder about evenly split between canola oil, animal fats, used cooking oils, and distillers corn oil.