The influence of small additions of the solutes Sn, Pb, Cu, Ag, and Ti on the diffusivity, solubility, activity, and the activity coefficient of oxygen in liquid indium was studied for temperatures between 750 and 950 °C, using solid state electrochemical techniques. A sharp increase in diffusivity and a decrease in solubility of oxygen were observed in all cases when small amounts of these solutes were added to liquid indium. Further additions of these solutes moderately increased the oxygen diffusivity and decreased the oxygen solubility. The thermodynamics of liquid binary alloys of indium, In-Sn, In-Pb, In-Cu, and In-Ag were also studied up to 10 at pct of these solutes. There is evidence that the large increase in diffusivity and decrease in solubility of oxygen in indium is due to cluster formations in liquid metal.