The surface charge densities of liquid In + Ga alloy electrodes with indium bulk contents ranging from 0 to 16.5 mol% were obtained as functions of the electrode potential by means of dropping microelectrode charging current and ac impedance measurements in aqueous 1 M NaClO4 solutions of varied pH at 32 degrees C. Using surface tension literature data of liquid In + Ga in vacuum and quasi-chemical multilayer model calculations they were integrated to electrocapillary curves. From the latter, the dependences of the indium surface excess on alloy composition, electrode potential and charge density were derived. A strong indium adsorption was found in the entire accessible range of bulk compositions. It extends over several atomic surface layers and can be accounted for by the surface tension difference between pure liquid gallium and indium, combined with the positive heat of mixing of the liquid In + Ga alloy system. It is shown that the indium surface excess decreases if the electrode potential or surface charge density is made more negative. A qualitative explanation in terms of pure component work function differences is given.