Effects of the fine structure of atomic oxygen on the O+-O ion-neutral momentum transfer collision frequency &ngr;in are investigated to assess whether they could account for persistent discrepancies between theoretical calculations and values of &ngr;in determined from observations. Potential curves for the molecule have been calculated that include spin-orbit effects and properly dissociate to the three asymptotic limits O+-O(3PJ) (J=2,1,0). Coupled channel scattering calculations have been performed to determine &ngr;in. The results show that &ngr;in depends strongly on the initial fine structure level, and the average over a thermal distribution of initial states is a few percent smaller than recent theoretical calculations that neglect fine structure effects. The most recent analysis of observations leads to values of &ngr;in about 30% smaller than older values. The theoretical calculations are now consistent with the most recent experimental determinations of &ngr;in.¿ 1997 American Geophysical Union