The vertical electronic spectra of the ion O− 2 and superoxides LiO2 and NaO2 are studied at the multireference configuration interaction (MRCI) level. For isolated O− 2 (with a ground state X2Πg(2σ2 g1π4 u1π3 g)), the present calculations place 12Πu(1πu → 1πg) at 5.20eV, 12Σ+ g(2σg → 1πg) at 6.32 eV and 22Σ+ u(1σu → 1πg) at 15.62eV, confirming the assignments made on the basis of electron scattering experiments on O2(X3Σ− g). An absorption band at 6.41 eV observed for O− 2-doped KC1 crystals is reassigned to 1πg → 2σu states of O− 2, instead of a charge-transfer excitation O− 2 → K+. A strong absorption band near 5.5eV for NaO2 crystals is confirmed to correspond to a π → π* (2B1 ← X2A2) excitation localized on the O− 2 moiety (f value ≈ 0.078 and vertical ΔE = 5.28 eV). Another band at 3.8 eV for NaO2 crystals, previously assigned to 12 Δu X2Πg of O− 2, is reassigned to charge-transfer states 1πg(O− g) → 3s, 3px, 3p y (Na+) with vertical ΔE's from 3.95 to 4.45eV and f values from 0.008 to 0.023. No experimental data are available for LiO2. Our calculations assign to this radical a strong π → π* absorption, with ΔE = 4.71 eV and f ≈ 0.1. Next in intensity one finds the charge-transfer state occupying 2p y (Li+), with ΔE = 5.18eV and f ≈ 0.031. For LiO2 and NaO2, the transition 12B2 ← X2A2 is of very low intensity (f ≤ 10−3) as it involves the components of the 1πg MO of O− 2 (i.e. both the transition moment and ΔE are small).