The kinetics of the reactions of O - and O 2 - with O 2(a 1Δ g) have been studied at 300 K in a selected ion flow tube (SIFT). The O 2(a 1Δ g) concentrations have been determined using emission at 1270 nm from the O 2(a 1Δ g, v = 0 → X 3σ g -, v = 0) transition measured with an InGaAs detector calibrated against absolute spectrally dispersed emission measurements. The rate constants measured for O - and O 2 - are 1.1 × 10 -10 and 6.6 × 10 -10 cm 3 s -1, respectively, with uncertainties of ±35%. The O 2 - reaction only produces electrons and can be described as Penning detachment, while the O - reaction has been found to produce both O 2 - and e -. The O 2 - branching fraction has a lower limit of ∼0.30. Comparison of the present results to previous measurements found in the literature provides a resolution to a previous discrepancy in the rate constant values.