The UV absorption spectrum and kinetics of the self reaction of CH₃OCH₂O₂ at 298 K have been studied using both the modulated photolysis of Cl₂/CH₃OCH₃/O₂/N₂ mixtures and the pulse radiolysis of SF₆/CH₃OCH₃/ O₂ mixtures. The spectrum, characterized in the range 200-290 nm, is in good agreement with the single published determination.⁸ The observed second-order removal kinetics of CH₃OCH₂O₂, k_5obs, were found to be sensitive to both the variation of total pressure (17-760 Torr) and the composition of the reaction mixtures: 2CH₃OCH₂O₂ → 2CH₃OCH₂O + O₂ (5a); → CH₃OCHO + CH₃OCH₂OH + O₂ (5b). The kinetic studies and a detailed product investigation using long path length FTIR spectroscopy (T = 295 K; Cl₂/CH₃OCH₃/ O₂/N₂ system) provide evidence to support a mechanism involving the rapid thermal decomposition of CH₃-OCH₂O by H atom ejection occurring in competition with the reaction with O₂: CH₃OCH₂O (+M) → CH₃OCHO + H (+M) (6); CH₃OCH₂O + O₂ → CH₃OCHO + HO₂ (4). The complications in the measured values of k_5obs in the present studies, and those reported previously, 8 are believed to occur as a direct result of formation of H atoms from reaction 6. Accordingly, a pressure-independent value of k₅ = (2.1 ± 0.3) × 10^-12 cm³ molecule^-1 s^-1 is derived for the elementary rate coefficient at 298 K, with identical values of the branching ratio α = k_5a/k₅ = 0.7 ± 0.1 determined independently from the FTIR product studies and the modulated photolysis experiments. As part of this work, the rate coefficient for the reaction of Cl atoms with CH₃OCH₂Cl was found to be (2.9 ± 0.2) × 10^-11 cm³ molecule^-1 s^-1.