The effect of implantation conditions on the localization of oxygen implanted with substoichiometric doses has been studied. Oxygen ions were implanted into Si wafers coated with a thin oxide film, which was etched off after the implantation. We used various implantation modes. After the implantation, the specimens were studied using SIMS and X-ray diffractometry. The concentration profiles suggest that at the lower implantation temperature, part of oxygen migrates toward the Si-SiO2 interface. The effect does not refer to the usual enhancement of SIMS signal at the surface because the concentration peak is at a depth of about 25 nm. Calculated deformation profiles indicate a compression at the same depth, the effect being the strongest for the low current density. The result suggests that the superficial layer is rich in vacancial-type defects. The coincidence of the deformation and oxygen concentration maxima leads to the conclusion that oxygen migrates toward the surface in the form of A-centers. A similar phenomenon has been observed for sequential low-temperature implantation of oxygen and nitrogen.