Synthetic spectra have been calculated incorporating three O₂ emission systems, A³Σ_u⁺ → X³Σ_g⁻, A′³Δ_u → a¹Δ_g, and c¹Σ_u⁻ → X³Σ_g⁻, and matched to the 3100‐ to 4500‐Å nightglow spectrum of Broadfoot and Kendall (1968). The synthesis necessitated the inclusion of the c¹Σ_u⁻ → X³Σ_g⁻ system, which has never been previously identified in the airglow, although it is a dominant system in the Venusian nightglow. The emissions from the extremely metastable A′³Δ_u and c¹Σ_u⁻ states account for half the radiation in the 3100‐ to 4500‐Å region, from which it may be deduced that the mesospheric concentrations of O₂(A′³Δ_u) and O₂(c¹Σ_u⁻) are much higher than that of O₂(A³Σ_u⁺). The vibrational distributions are quite unrelaxed for all three states.