The potential energy surfaces of the reactions CCl 2 +O 2 (3 Σg) and CCl 2 + O 2 (1  g) were investigated by quantumchemical calculations. The geometry and energy of the reactants, intermediates and products were characterized employing different formulations of the density functional theory (DFT), with the Pople's basis set 6-311+G(3df). The mean value of the barrier height for the reaction CCl 2 + O 2 (3 Σg) is E 0 # = (7,1 ± 2,7) kcal mol-1 , and the reaction of the CCl 2 with O 2 (1  g) proceeds without a barrier. A crossing region of the triplet and singlet potential energy surfaces was found.