Upward flowing fluxes of energetic (0.5--16 keV) H+ and O+ ions are frequently observed by the ion mass spectrometer on the polar-orbiting S3-3 satellite. Data obtained on the first ~370 orbits have been used to derive the occurrence frequency of these fluxes. The upward acceleration of ionospheric ions to keV energies is persistent phenomenon generally occurring in a zone closely associated with the statistical auroral oval. Upward flowing ion events with flux above ~2¿106 keV/(cm2 sec ster keV) are observed in more than 60% of the orbits. A strong dawn-dusk asymmetry is found in the frequency of occurrence with the maximum in the dusk sector. The probability of observation increases with altitude up to apogee (8000 km) indicating that the main energization takes place preferentially at altitudes above ~1 RE.