When O₂ is perturbed by collisions with other molecules, the weak spin-forbidden magnetic dipole transition a¹Δ_g←X³Σ_g⁻ shows a broad continuum absorption underlying the sharp lines. This collision-induced enhancement absorption plays a role in the Earth’s atmosphere and much experimental work has been carried out to measure the binary absorption coefficient with different perturber gases. Recent work on the v′=0←v=0 band in O₂–CO₂ mixtures yielded a value for the coefficient that was approximately three times that of earlier measurements on O₂–N₂ mixtures. In the present note, we calculate the absorption theoretically assuming that the long-range quadrupole-induced dipole mechanism is dominant. Using experimental polarizability matrix elements of CO₂ and ab initioresults in the literature for the quadrupolar transition matrix element for O₂, we find good agreement for O₂–CO₂ mixtures without any adjustable parameters. The agreement for O₂–N₂ is less good, and because of the much smaller polarizability of N₂ than of CO₂, we suggest that one has to include a short-range component in addition to the long-range one treated here. We also calculate the binary absorption coefficient for O₂–H₂O, for which no experimental data are available, and we synthesize the corresponding spectrum for use in atmospheric modeling.