Ab initio calculations have been performed for the four singlet states of (O-2)(2) dissociating into O-2((1)Delta(g)) + O-2((1)Delta(g)). They are compared with previous semi-ab initio perturbation calculations. A surprisingly good agreement in the potential behavior is observed between these two complementary treatments. After the recent work of Minaev et al., these are the first ab initio calculations of the excited states of the dimer, corrected for basis set superposition errors (BSSE) and evaluated in a size consistent way. Though a similar behavior of the potential with the intermolecular distance has been observed by Minaev et al., discrepancies remain in the binding energies of the dimer.