The role of oxygen concentration on the formation/evolution of residual defects in implanted and rapid thermal annealed silicon was studied in samples with various oxygen concentrations. Photoluminescence (PL) study showed a strong correlation between the D-line intensity and the oxygen concentration. Transmission electron microscopy (TEM) measurements also suggested the extended defects were more favored in the high oxygen sample. High frequency capacitance-voltage (C-V) measurements revealed excess acceptors that were further investigated by deep level transient spectroscopy (DLTS). A hole trap with activation energy of 450 meV was detected and was suggested to relate to agglomerations of point defects associated with more than one type of 3D-metal related deep levels.