Reactions involving metastable ions are difficult to study in the laboratory. Much new information on these reactions has been derived from satellite measurements of aeronomic parameters. In this paper we use Atmosphere Explorer D data to study charge exchange of metastable O+(2D) ions with O2. Using direct measurements of the O2 at 200 km to compute O2 densities at 300 km and supporting ionic concentrations and temperature observations, we find the rate coefficient for this reaction to be 1¿0.6¿10-9 cm3 s-1. The process constitutes a significant source of O2+ ions in the F2 layer at times when the N2 and O2 densities are enhanced. This finding leads to the conclusion that charge exchange with O2 must be a major sink for O+ (2D) and an important source of O2+ ions in the E region, because of the increase in the [O2>/[N2> ratio with decreasing altitude. The results imply that 80% of all O+ ions formed in the E region are converted to O2+ and that only ~20% of the metastable O+ ions are converted into N2+ through charge exchange with N2.