Diesel fuel made from natural renewable sources such as vegetable oils or animal fats lowered air-polluting emissions of heavy trucks in a study conducted by the National Renewable Energy Laboratory (NREL). Biodiesel fuel can be used in regular diesel engines without equipment modification.

The scientists studied a blend of 35 percent biodiesel fuel and 65 percent conventional diesel fuel. They found that this emitted significantly less carbon monoxide and moderately less hydrocarbons and particulate matter, compared to 100 percent petroleum diesel.