Fourier transform spectroscopic measurements of the absorption bands of the Herzberg III (A' (3)Delta(u)-X (3)Sigma(g)(-)) of O-2 at 295 K have been made with a resolution of 0.06 cm(-1) in the wavelength region 240 to 275 nm. Rotational line positions are determined with an accuracy of 0.005 cm(-1), and rotational term values are presented for the vibrational levels, v'=4-11. Precise band oscillator strengths of the (4,0)-(11,0) bands are obtained for the first time by direct measurement by summing the cross sections of individual rotational lines of the bands. The rotational line strengths and the branching ratios are also presented for the same bands. The continuity relationship for the band oscillator strengths to photodissociation continuum cross sections has been applied to the three-band systems.