Remote argon plasma (RP) and ozone in the presence of ultraviolet light (UV–O3) were used to render polystyrene (PS) surfaces hydrophilic in a controlled manner for eventual application in cell-surface interaction studies. X-ray photoelectron spectroscopy (XPS) was used to characterize both methods of modification. The degree of modification on PS was measured by an increase in surface oxygen and concomitant change in C 1s binding energies as a function of time. Both remote plasma and UV–O3 are shown to be partially surface destructive, producing polymer fragments which are easily washed away to leave stable modified surfaces of oxidized polymer comprising of distributions of C–O, C=O and O—C=O type groups. Of the two methods, UV–O3 is shown to be more versatile and conducive to preparing PS surfaces with controllably varying degrees of modification. UV–O3 modified polystyrene is shown to be stable in air for at least eight months. Contact angle methods were used in correlation with XPS in characterizing UV–O3 modified surfaces. It is shown that changes in surface tension and total surface oxygen content were related, however, not directly connected.