In the past few years, scientists have found several new fuels to replace gasoline for automobiles. One of these fuels is methanol, a form of wood alcohol. It can be used in many cars in almost the same way that gasoline is used. Natural gas is another alternative fuel for cars. However, cars that burn this fuel must be equipped with special tanks of natural gas. A third alternative is electricity. Cars fueled by electricity have no engine at all, though they do have to carry large batteries. A fourth new energy source, and perhaps the most promising, is the hydrogen fuel cell. Hydrogen is available in large quantities, and the fuel cell's only emission is a small amount of water.