Fuels produced from plant sources, such as ethanol derived from corn. Biofuels have been around since the start of the 20th century. Henry Ford had planned to power his early Model T cars with ethanol. Early diesel engines were shown to run on peanut oil. Discoveries of vast petroleum deposits made gas and diesel cheaper than biofuels which is why they were eventually forgotten. But with the recent rise in oil prices and concern about carbon dioxide emissions, biofuels are regaining popularity. See also biodiesel.