Gasoline is a blend of hydrocarbons with some contaminants, including sulfur, nitrogen, oxygen, and certain metals. The four major constituent groups of gasoline are olefins, aromatics, paraffins, and napthenes. The main alternative fuels include alcohol, liquefied petroleum gas, compressed natural gas, hydrogen, and electricity for operation gasoline-type vehicles. Ethanol and methanol are biofuels that provide alternatives to gasoline. Bioethanol is a fuel produced by processing familiar and renewable crops such as cereals, sugar beet, and maize using natural fermentation. Blended with petrol at 10%, bioethanol can be used in vehicles without the need to change fuel or engine specifications.