Methanol, CH₃OH, a compound that can be made relatively inexpensively from coal, is a promising substitute for gasoline. The alcohol has a smaller energy content than gasoline, but, with its higher octane rating, it burns more efficiently than gasoline in combustion engines. (It has the added advantage of contributing to a lesser degree to some air pollutants.) Compare the enthalpy of combustion per gram of CH₃OH and C₈H₁₈ (isooctane), the latter being representative of the compounds in gasoline. (∆_fH° = −259.3 kJ/mol for isooctane.)