The aqueous phase oxidation kinetics of sulfur(IV) by hydrogen peroxide, methylhydroperoxide, and peroxyacetic acid have been investigated over the pH range 4.0--5.2 for hydrogen peroxide and methylhydroperoxide and 2.9--5.8 for peroxyacetic acid. The reagent concentrations used in these studies were in the micromolar range. In the cases of hydrogen peroxide and peroxyacetic acid, 1 mol of sulfate was produced for each mole of peroxide consumed. ln the case of methylhydroperoxide, 0.73¿0.04 mol of sulfate, and 0.27¿0.04 mol of the methylsulfate were produced for each mole of peroxide consumed. The experimentally determined rate laws for the three reactions are given by d/dt=k+>peroxide>. The third order rate constants, k, for the three reactions were determined to be 7.2¿2.0¿107 M-2 s-1 for hydrogen peroxide (18¿C) 1.7¿0.4¿107 M-2 s-1 for methylhydroperoxide (23¿C), and 3.5¿1.3¿107 M-2 s-1 for peroxyacetic acid (18¿C). The oxidation kinetics of aqueous S(IV) by peroxyacetic acid also contained a second-order term over the pH range investigated in this study, first-order in both peroxyacetic acid and S(IV) concentrations. The rate constant k' for this term was determined to be 6.1¿2.6¿102 M-1 s-1. Temperature dependence studies over the range 6¿--25¿C yielded activation energies of 31.6¿1.3 kJ/mol for methylhydroperoxide and 33.2¿0.7 kJ/mol for peroxyacetic acid. ¿American Geophysical Union 1987