The photoabsorption cross section of O2 in the Schumann-Runge bands is investigated theoretically using the coupled-channel Schr¿dinger-equations method. It is found that quantum interference between vibrational bands leads to significant asymmetry in the far line wings, a result supported by experimental evidence. Thus, Schumann-Runge cross sections calculated with the usual band models based on Voigt line shapes may be in error in regions of weak absorption between vibrational band heads, suggesting the need to re-evaluate aspects of atmospheric photochemistry sensitive to those regions. ¿ 1998 American Geophysical Union