Measurements of ring current ion densities by the Active Magnetospheric Particle Tracer Explorers CCE satellite suggest that a large flux of energetic (tens of keV) O+ precipitates in the mid-latitude atmosphere during major geomagnetic storms. The mass spectrometer (>30 keV) on board the NOAA 6 satellite measured an ion flux of 30 ergs cm-2 s-1 at 52¿ invariant latitude during a very large geomagnetic storm. To calculate atmospheric response to precipitation of the energetic O+ fluxes, we have revised an O+ transport model to include energies up to 200 keV. The model's sensitivity to the estimated cross sections and model atmosphere for various monoenergetic O+ fluxes are presented in this paper. Calculations of the atmospheric response to O+ precipitation shows that (1) most of the incident energy is immediately transformed into atmospheric heating, (2) the total number of escape particles is smaller than the total number of incident particles, in constrast to the results of previous models, and (3) the peak heating and ionization altitudes vary from 104 to 300 km depending on the incident energy. The results are most sensitive to the estimated differential scattering cross sections at large scattering angles. The use of forward scattering cross sections at both extremes of the possible range results in very different energy allocations and altitudes of peak ionization and heating (a difference of as much as 80 km). The MSIS-86 model atmosphere with extreme parametric values caused little change in the energy allocation, but the large variations in the model atomic oxygen density (F10.7 index=70 and 210) alters the peak heating and ionization altitude for low-energy incident O+ (a few keV) by 50 km. ¿American geophysical Union 1992