A mass and energy resolved photoion spectrum of O-2 induced by 12 ns 193 nm radiation with an intensity of 10(10)-10(11) W/cm(2) is presented. The analysis of the spectrum gives (1) the two-photon ionization cross section (approximate to 1.1X10(-54) cm(4) s) of the X (3) Sigma(g)(-) of O-2 and (2) the intensity dependent branching ratios between photoionization and predissociation of the B (3) Sigma(u)(-) state of O-2 The two-photon ionization cross section of O-2 is linked to our ab initio calculation of the three-photon ionization cross section (approximate to 7.5X.10(-84) cm(6) s(2)) of atomic oxygen.