The reactions of C2H5 With O, O-3, and NO3 have been investigated in a discharge flow reactor at room temperature and pressures between 1 and 3 mbar. The reaction products were detected by mass spectrometry with electron-impact ionization. The product pattern observed is explained in terms of the decomposition of an intermediately formed, chemically activated ethoxy radical. It is shown that, with this assumption, the experimentally determined branching ratios of the different product channels can be reproduced nearly quantitatively by RRKM calculations based on ab initio results for the stationary points of the potential energy surface of C2H5O For C2H5 + O and C2H5 + O-3, the existence of an additional, parallel channel leading to OH has to be assumed. High-pressure Arrhenius parameters for the unimolecular reactions of the ethoxy radical are given and discussed.