Biodiesel made from oil seed plants grown on cropland cannot possibly hope to replace petro-diesel in the foreseeable future: there simply isn’t enough land. Biodiesel, instead, could be seen as one part of a larger plan to reduce air pollution, carbon emissions, and dependence on fossil fuels. Energy crops can also be an important source of income for farmers.

Scientists are currently researching ways to produce biodiesel using new feedstocks that are less limited by the availability of land. For example, some types of algae can produce oil. Energy crops could also be grown on land that is not suitable for food crops, such as soil that is too acidic or too salty, that has too many minerals or is too shallow, or that is in danger of eroding. In these cases, energy crops might help stabilize and restore this land.

Scientists are also experimenting with producing fuel from non-oil seed feedstocks such as inexpensive, non-edible biomass (agricultural residue, waste from the wood products industry, and switchgrass and other grasses) that can be converted into a diesel replacement. While it is a fairly simple process to convert vegetable oil or animal fat into biodiesel, the conversion of cellulosic feedstocks to fuel is more complicated and more expensive. To produce a hydrocarbon fuel, the biomass is generally first converted into a synthetic gas using high heat. Then the gas can be converted into a liquid diesel fuel.

The fuel resulting from these new technologies is technically not “biodiesel,” which is defined, according to the ASTM specifications, as “mono-alkyl esters of long chain fatty acids derived from vegetable oils or animal fats.” Instead, these fuels from cellulosic feedstocks are termed “renewable diesel” or “green diesel.” This term also includes fuels produced from vegetable oils and animal fats using conventional petroleum-refining techniques.