The effect of pressurized foreign gases on the photoabsorption of O-2 in Herzberg bands and the Herzberg continuum was studied. The values of the cross section in O-2 and O-2/N-2 mixtures under various pressures were in good agreement with the results in previous literature. The absorption of O-2 in CO2, methane, ethane, and ethylene was found to increase considerably with cross sections proportional to the number density of the foreign gases. The "density coefficient" of the absorption cross section was determined for individual foreign gases. A good correlation was found between the coefficient and the foreign gas ionization potential, which implies the contribution of charge-transfer-like interaction between O-2 and the foreign gas for relaxing the dipole-forbidden transition.