Synthetic spectra have been calculated incorporating three O2 emission systems, A3&Sgr;u +→X3&Sgr;g -, A'3Δu→a1Δg, and c1&Sgr;u -→X3&Sgr;g -, and matched to the 3100- to 4500-¿ nightglow spectrum of Broadfoot and Kendal (1968). The synthesis necessitated the inclsuion of the c1&Sgr;u -→X3&Sgr;g - system, which has never been previously identified in the airflow, although it is a dominant system in the Venusian nightglow. The emissions from the extremely metastable A'3Δu and c1&Sgr;u - states account for half the radiation in the 3100- to 4500-¿ region, from which it may be deduced that the mesospheric concentrations of O2(A'3Δu) and O2(c1&Sgr;u -) are much higher than that of O2(A3&Sgr;u +). The vibrational distributions are quite unrelaxed for all three states.