The potential energy surfaces of neutral methanol oxide and dimethyl ether oxide and their anion and cation radicals have been calculated at the BECKE3LYP/6-311++G(d,p) level of theory. Both neutral singlet methanol and dimethyl ether oxides are predicted to correspond to local minima on their potential energy surfaces. Natural bonding orbital (NBO) population analysis reveals a distinct ylidic character for these species. Upon increasing methyl substitution, the R2O+-O-ylide structure is stabilized energetically because of the better charge distribution of the formally positive central oxygen atom; thus, the energy differences relative to the R2O + O-3 exit channel decrease significantly. The barrier for the 1,2-hydrogen migration in methanol oxide to yield methyl hydroperoxide amounts to only 5 kcal/mol, whereas the methyl shift in dimethyl ether oxide to afford dimethyl peroxide demands >40 kcal/mol and can proceed by retention or inversion of the configuration at the migrating carbon. The kinetic stabilization of the latter is instead determined either by the loss of a methyl radical or by spin crossing to the triplet surface followed by O atom loss. For this process, the minimal-energy crossing point of the two neutral surfaces was located. The corresponding cation radicals of methanol and dimethyl ether oxide rest in rather deep wells, and their geometries are not too different from those of the neutrals, Therefore, neutralization-reionization mass spectrometry may allow generation and identification of the neutral species, provided that the cation-radical precursors can be made. Furthermore, the kinetic stability of neutral dimethyl ether oxide may be sufficient for its detection in matrix isolation experiments.