A fuel tax (also known as a petrol, gasoline or gas tax, or as a fuel duty) is an excise tax imposed on the sale of fuel. In most countries the fuel tax is imposed on fuels which are intended for transportation. Fuels used to power agricultural vehicles, and/or home heating oil which is similar to diesel are taxed at a different, usually lower rate. The fuel tax receipts are often dedicated or hypothecated to transportation projects so that the fuel tax is considered by many a user fee. In other countries, the fuel tax is a source of general revenue. Sometimes, the fuel tax is used as an ecotax, to promote ecological sustainability.