The absorption spectra of the O2 Herzberg band systems (A3Σ+u-X3Σ -g, c1Σ-u-X3Σ -g, and A′ 3Δu-X3Σ-g) lying in the wavelength region 240-300 nm were reinvestigated. The coupling of a long absorption cell and a high-resolution Fourier transform spectrometer has allowed the observation of numerous weak lines which were not reported previously. From the rotational analysis of the line positions, determined with an accuracy of 0.005 cm-1, the molecular constants of the A3Σ+u, v = 0-12, c1Σ-u, v = 2-19, and A′ 3Δu, v = 2-12 levels are improved significantly. The interaction between the A and c states is described quantitatively. A new interpretation of the perturbations observed in the energy region close to the dissociation limit is given which involves a weakly bound 3Πu state as the most probable perturbing state.