An impinging jet electrochem. flow cell developed for use with bead type electrodes was successfully employed in a surface structure sensitive study involving the processes of CO adsorption and oxidn. on Pt(111) in 1.0 mol dm-3 H2SO4 and HClO4. The flow cell enabled straightforward CO coverage control by means of varying the dosing time. Anion and hydrogen displacement charge curves with high potential resoln. were obtained by means of CO adsorption and an electrolyte dependent fine structure was found. During the dosing of the electrolyte dissolved CO in the potential range 700-800 mV (vs. RHE) a slow delayed oxidn. of adsorbed CO was noted and interpreted as being due to adsorption competition between CO and an oxygen contg. species. A novel anion-anion displacement method was developed in which adsorbed bisulfate was replaced by perchlorate or water. The neg. current transient obtained indicated desorption of bisulfate.