The reactions of thirteen CmHn+ ions (m less than or equal to 6) with atomic and molecular oxygen and nitric oxide have been measured using a selected ion flow tube operating at room temperature. Rate coefficients and product distributions are reported for each reaction. Most of the hydrocarbon ions studied exhibit relatively rapid reactions with O atoms and proceed at substantial fractions of the collision rate. All O atom reactions showed multiple product channels and the formation of a -C-O bond, either in the ion product or the neutral product of reaction. (C) 2000 American Institute of Physics. [S0021-9606(00)00811-4].