MTBE, or Methyl Tertiary Butyl Ether, is an ether compound used as a gasoline blending component since 1979. MTBE is made by combining isobutylene and methanol. Originally, it was used to help raise the octane of gasoline. It is also used to raise the oxygen content of gasoline to meet government mandates. However, because of environmental concerns, in the United States, MTBE has been widely replaced by ethanol as an oxygenate.