Cold model experiments are carried out to understand the spout eye area in a cylindrical bath agitated by bottom gas injection. Low-density particles are used for slag to investigate the effect of a density ratio of molten slag to molten steel on the spout eye area. The spout eye area increases with a decrease in the density ratio and is governed by the same modified Froude number as that proposed for a silicone oil and mercury system. An empirical equation is proposed for the spout eye area.