The kinetics of the reactions of O- and O-2(-) with O-2(a(1)Delta(g)) have been studied at 300 K in a selected ion flow tube (SIFT). The O-2(a(1)Delta(g)) concentrations have been determined using emission at 1270 nm from the O-2(a(1)Delta(g), v = 0 -> X-3 Sigma(-)(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 x 10(-10) and 6.6 x 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 similar to 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.