The kinetics of the reactions of ethene and propene with triplet oxygen atoms have been studied over a wide temperature range, T = 230–900 K, using a low-pressure (P = 1 Torr) flow tube reactor coupled with an electron impact ionization quadrupole mass spectrometer: O + C2H4 → products (1) and O + C3H6 → products (2). The rate constants of the title reactions were determined under pseudo–first-order conditions, either monitoring the kinetics of O-atom consumption in excess of alkene or alkene loss in excess of oxygen atoms. The temperature dependence of the rate constant of reaction (1), k1 = 8.64 × 10−17 T1.70 exp(–206/T) cm3 molecule−1 s−1 (uncertainty of 20%), was found to be in excellent agreement with multiple previous data that can be considered as a validation of the experimental approach. The measurements of the rate constant of the reaction of O atoms with propene, k2 = 3.65 × 10−18 T2.20 exp(455/T) cm3 molecule−1 s−1 (uncertainty of 20%), allowed to harmonize the results of previous low- and high-temperature measurements and to recommend the expression for k2 in a wide temperature range, 200–1200 K