The kinetics and mechanism of the reaction of atomic chlorine with ethyl formate [Cl + CH3CH2O(C=O)H, reaction 1] have been examined. These experiments were performed at pressures of 760-950 Torr and temperatures from 297 to 435 K. Reactants and products were quantified by gas chromatography-flame ionization detector (GC/FID) analysis. The initial mixture contained ethyl formate, Cl-2, and N-2. Cl atoms were generated by UV photolysis of this initial mixture at 360 nm, which dissociates Cl-2. The rate constant of reaction 1 was measured at 297 K relative to that of the reaction Cl + C2H5Cl (reaction 2), yielding the rate constant ratio k(1)/k(2) = 1.09 +/- 0.05. The final products formed from reaction 1 are ethyl chloroformate, 1-chloroethyl formate, and 2-chloroethyl formate. These products result from the reactions with Cl-2 of the three free radicals formed by H atom abstraction from ethylformate in reaction 1. Based on the molar yields of these three chlorinated products, the yields of the three radicals formed from reaction 1 at 297 K are (25 +/- 3) mole percent of CH3CH2O(C=O); (67 +/- 5) mole percent of CH3CHO(C=O)H; and (8 +/- 2) mole percent of CH2CH2O(C=O)H. A second phase of this experiment measured the rate constant of the decarboxylation of the ethoxy carbonyl radical [CH3CH2O(C=O) -> CO2 + C2H5, reaction 4] relative to the rate constant of its reaction with Cl-2 [CH3CH2O(C=O) + Cl-2 -> CH3CH2O(C=O)Cl + Cl, reaction 3a]. Over the temperature range 297 to 404 K at 1 atm total pressure, this ratio can be expressed by k(4)/k(3a) = 10(23.56 +/- 0.22) e(-(12700 +/- 375)/RT) molecules cm(-3). Estimating the value of k(3a) (which has not been measured) based on similar reactions, the expression k(4) = 5.8 x 10(12) e-((12700)/RT) s(-1) is obtained. The estimated error of this rate constant is +/- a factor of 2 over the experimental temperature range. This rate expression is compared with recent ab initio calculations of the decarboxylation of the analogous methoxy carbonyl radical.