Reactions of Ar+ ions with H2, N2, O 2, CO CO2, N2O, and COS have been meausred in a flow-drift tube at center-of-mass energies of 0.04-2.5 eV. The reactions with H2 and COS are fast and show only small energy dependences. The reaction with N2 is very slow at thermal energies and the rate coefficient increases very fast with increasing energy. The rate coefficients for the reactions with CO2 and N2O decrease with increasing energy over the whole energy range studied. For the reactions with O2 and CO, we find minima of the rate coefficient at 0.4 and 0.8 eV, respectively, followed by a dramatic increase at higher energies.