Ab initio computational methods have been employed to determine the frequency-dependent polarizabilities of both the first excited (a(1)Delta(g)) and ground (X(3)Sigma(g)(-)) states of molecular oxygen. Polarizabilities are reported for oxygen in the gas phase as well as under both equilibrium and nonequilibrium conditions in four solvents. The data consistently show that, for any set of comparable solvation conditions, the polarizability of O-2(a(1)Delta(g)) is smaller than that of O-2(X(3)Sigma(g)(-)). This phenomenon differs from that observed with most other molecules, where the polarizability of the excited state is typically much larger than that of the ground state. The results reflect unique changes in the orbital occupancy associated with electronic excitation in the oxygen molecule. The consequences of this finding are important, particularly with respect to the interpretation of the solvent effect on radiative transitions in oxygen.