Rate coefficients and product distributions have been measured using a selected ion flow tube for reactions of the ions HnC3O+ (n = 0-3) and C3O2+ with the neutral species H-2, CO, N-2, O-2, CH4, NH3, H2O, C2H2, HCN, and CH3CCH at 300 K. The structures of the ions are discussed, and a survey af relevant enthalpies of formation is presented.