The Cl-atom initiated oxidation of ethyl chloride and ethyl bromide has been investigated as a function of temperature (220-298 K) in an environmental chamber equipped with an FTIR spectrometer. In the absence of NOx, reaction with O-2 (CH3CHCIO + O-2 --> CH3C(O)Cl + HO2, reaction 9) and decompositon via HCl-elimination (CH3CHCIO --> CH3CO + HCl, reaction 8a) are shown to be competing fates of the CH3CHCIO radical generated in the ethyl chloride system, with k(9)/k(8a) = 3.2 x 10-(24) exp(2240/T) cm(3) molecule(-1). The CH3CHCIO radical is also shown to be subject to a chemical activation effect; when produced in the exothermic reaction of CH3CHCIO2 with NO, about 50% of the nascent CH3CHClO radicals decompose promptly via HCI elimination, before collisional. deactivation can occur. The reaction of Cl with ethyl bromide occurs 70-80% via abstraction from the -CH2Br group and 20-30% via abstraction from the -CH3 group. The observation of ethene in this system indicates that the BrCH2CH2 radical (generated via abstraction from the -CH3 group) undergoes Br-atom elimination (BrCH2CH2 - CH2=CH2 + Br, reaction 37) in competition with its reaction with O-2 (BrCH2CH2 + 02 - BrCH2CH2O2, reaction 34) At atmospheric pressure, this competition is governed by the rate coefficient ratio, k(37)/k(34) = 1.4 x 10(23) exp(-2800/T) molecule cm(-3). The chemistry of the CH3CHBrO radical (generated from abstraction at the -CH2Br site) is dominated by Bratom elimination; no evidence for its reaction with O-2 could be found at any temperature.