Rayleigh scattering of solar radiation by oxygen molecules is an important contributor to the photon flux in the atmosphere at wavelengths longer than the threshold for direct photodissociation of O2 near 180 nm. We carry out detailed calculations of Rayleigh scattering cross sections of O2 at wavelengths from 180 to 205 nm in the region of the discrete Schumann-Runge band system. The cross sections contain numerous resonance structures, whose characteristics we identify. Beyond 205 nm we show that the cross sections diminish rapidly before taking up the known variation as the inverse fourth power of the wavelength at long wavelengths. We present detailed results for cross sections for scattering by O2 in individual rotational levels of the ground vibrational state sufficient to allow the calculation of the Rayleigh scattering cross sections at atmospheric temperatures.