The ns (n=4-9) and nd (n=3-8) Rydberg states of O-2 converging on O-2+ X (2)Pi(1/2g) and X (2)Pi(3/2g) have been studied using optical-optical double resonance via single rotational levels of the initially excited b (1)Sigma(0g)(+) valence state, together with multiphoton ionization. Both ns and nd states show a transition from (Lambda,S) coupling to (Omega,omega) coupling as n increases. Transitions to all four components of an ns cluster are observed and rotational linestrengths show that the ns (3)Pi(2,1,0g)+<--<--b (1)Sigma(0g)(+) transitions borrow intensity from the ns (1)Pi(1g)<--<--b (1)Sigma(0g)(+) transition. (C) 2003 American Institute of Physics.