Methyl-t-butyl-ether (MTBE) has become a prevalent groundwater pollutant due to its high volume use as a nationwide gasoline additive. Given its physicochemical properties, it requires new treatment approaches. Both aqueous O-3 and a combination of O-3/H2O2, which gives .OH, can remove MTBE from water, making use of O-3 a viable technology for remediation of groundwater from fuel contaminated sites. Rate constants and temperature dependencies for reactions of MTBE with O-3 or with .OH at pH 7.2, in a range of 21-45degreesC(294-318 K) were measured. The second-order rate constant for reaction of MTBE with O-3 is 1.4 x 10(18) exp(-95.4/RT) (M-1 s(-1)), and for reaction of MTBE with .OH produced by the combination of O-3/H2O2 is 8.0 x 10(9) exp(-4..6/RT) (M-1 s(-1)), with the activation energy (kJ mol(-1)) in both cases. At 25degreesC, this corresponds to a rate constant of 27 M-1 s(-1) for ozone alone, and 1.2 x 10(9) M-1 s(-1) for O-3/H2O2. The concentration of .OH was determined using benzene trapping. Products of reactions of O-3 and O-3/H2O2 with MTBE, including t-butyl-formate (TBF), t-butyl alcohol (TBA), methyl acetate, and acetone, were determined after oxidant depletion. A reaction pathway for mineralization of MTBE Was also explored. Under continuously stirred flow reactor (CSTR) conditions, addition of H2O2 markedly increases the rate and degree of degradation of MTBE by O-3. (C) 2002 Elsevier Science B.V. All rights reserved.