Flash photolysis combined with time-resolved UV spectroscopy and transient IR absorption measurements shows that chlorine atoms react rapidly with CH3O2 and C2H5O2, producing ClO and CO among other products. The room temperature rate constants are k(2) = (1.5 +/- 0.2) X 10(-10) cm(3) s(-1) for both reactions. The distribution of products is interpreted to indicate that the reaction with methylperoxy radicals proceeds via two channels to yield CH3O + ClO with a branching ratio of 0.51 +/- 0.05 and CH2O2 + HCl with a branching ratio of 0.49 +/- 0.05. The Criegee intermediate, CH2O2, has a lifetime of 15 +/- 5 mu s and subsequently decomposes via three channels, with 61 +/- 7% producing CO + H2O. The ethylperoxy reaction proceeds analogously with a branching fraction of 0.49 +/- 0.05 for the C2H5O + ClO channel, but with a CO yield similar to 1/6 of the yield from the methylperoxy reaction.