Three previously unobserved paramagnetic centers: OX1, OX2, and OX3, have been revealed by the EPR studies of synthetic diamonds grown in Na2CO3–CO2–C system. All of these centers have electron spin S = 1/2 and have not got hyperfine structure. High g-factor anisotropy of the studied OX1, OX2, and OX3 centers in the absence of transition metal ions in diamond structure may be indicative that there is an oxygen atom in the structure of these defects. IR spectra of the studied diamonds contain intensive line at 1332 cm−1, which confirms high content of positive charge state of substitutional nitrogen (N+) in studied diamonds. It was supposed that all of these three centers have negative charge states. In the paper structures of OX1, OX2, and OX3 centers are discussed according to the obtained experimental data.