Gasoline /ˈɡæsəliːn/, or petrol /ˈpɛrəl/, is a toxic, clear liquid that is mostly used as a fuel in internal combustion engines. It is made by boiling petroleum, a fossil fuel. In a distillation process, petroleum is heated to a very high temperature, then it separates into its components, one of them is gasoline. This is an expensive process. It is made mostly of octane (C8H18), a hydrocarbon.