Methyl tert-butyl ether (MTBE), is an organic compound, chemical formula C5H12O, colorless transparent liquid, insoluble in water, soluble in ethanol, ether, is an excellent high octane gasoline additive and antiknock agent.

It is mainly used as gasoline additive, has excellent knock resistance, improves octane number, and can also be cracked to produce isobutene. It has good miscibility with gasoline, less water absorption, no pollution to the environment, can be improved as an analytical solvent, extractant, in chromatography especially high pressure liquid chromatography as a removal agent, and some polar solvents such as water, methanol, ethanol and other azeotrope formation. Mtbe also has a mild narcotic effect.