Ab initio configuration interaction calculations have been carried out for seven low-lying states of the oxygen molecule, Three different types of nonadiabatic couplings have been considered : spin-orbit, radial, and rotational. The complex scaling method has been employed to compute rovibrational level locations and predissociation linewidths with a basis of 200 Hermite polynomials for each of 13 different Omega electronic states. The calculations correctly predict that the nu = 2 level has the narrowest linewidth for the O-16(2) C (3) Pi(g) state, while nu = 4 is narrowest for O-18(2). Marked variations in the linewidths of the different Omega components of the C state are explained by the fact that the pi* --> 3s sigma Rydberg and sigma --> pi* valence (3) Pi(g) states have different occupations of the pi* orbital, causing opposite orderings of their respective Omega levels. Rotational, coupling is found to be important for high J values of the C state. The d (1) Pi(g) 3s sigma state shows ever more unusual effects by virtue of the fact that there is a sharply avoided crossing between the. corresponding Rydberg diabatic state with a bound sigma --> pi* (1) Pi(g) valence state. The calculations find irregular spacings in the d-state vibrational manifold, wide variations in linewidth for different nu,J levels, and a large change in the rotational constant in successive vibrational levels, all of which effects have been earlier demonstrated in experimental work. Satellite lines are indicated for both the nu = 2 and 3 levels as a result of the interaction with the bound (1) Pi(g) valence state, whereby experimental verification exists only for nu = 2. The nu = 3 state has not yet been successfully identified due to the broadness of the d-X spectrum in the energy range of interest. The observed temperature dependence of the linewidths of the two features near the expected location of the nu = 2 level can also be understood on the basis of these calculations. Finally, the change in the predissociation mechanism for the d state from spin-orbit to radial as nu changes from 0 to 2 which has been deduced experimentally is also verified in the present theoretical treatment.