Ion composition in substorm injections are investigated in detail by using data obtained from the magnetospheric ion composition spectrometer (MICS) on board the Combined Release and Radiation Effects Satellite (CRRES). A total of 398 injection events are identified from 4 February to 10 October, 1991. It is found that the flux enhancements of O+ ions in the with-oxygen injections (O+ ions occupy more than 20% of the total energy density) are attributed to the flux intensifications of high-energy (E/q ≥ 100 keV/e) ions. In contrast, the flux of H+ and He++ ions in the without-oxygen injections (O+ ions are less than 20% total energy density) are enhanced by the intensification of lower energy H+ and He++ (around 50 keV/e) ions. Statistical results also demonstrate that the abundance of O+ ions in an injection strongly depends on the geomagnetic activity. Without-oxygen events take place most probably in relatively weak geomagnetic activity conditions (Dst index is around -50 nT and Kp is around 4). The averaged fractional energy density of O+ ions increases roughly linearly with Kp index. All injections are found to be rich of oxygen ions during the strong magnetic storms (Dst < -100 nT). The present study indicates that the ionospheric oxygen ions are energized more readily during the storm conditions. When the near-Earth reconnection occurs and expands from the central plasma sheet to the plasma sheet boundary layer or even to the lobe region, much more ionosphere origin O+ ions could participate and be energized in the magnetospheric dynamic process. This leads to a with-oxygen injection in the inner magnetosphere. As to the without-oxygen injection, it seems that only preexisting oxygen ions in the near-Earth plasma sheet are accelerated and become a part of the injected ions, thus a rather low abundance of O+ ions can be observed.