Rate coefficients and product ion distributions have been determined for the reactions of HCNH+, HC3N+, H2C3N+, H2O+, N-2(+), HCO+, and HCO2+ with O atoms in a selected ion flow tube at 295 +/- 5 K. Only two of these ions, HC3N+ and N-2(+), were found to react with atomic oxygen, and both ions exhibited multiple reaction channels. Reactions with O atoms may be relevant to synthetic processes occurring in some interstellar clouds. Because of the application of the N + NO titration to determine O atom concentrations, the rate coefficient and product distribution for the reaction of each ion with O-2 and NO was also measured.