Two cold models were employed to simulate the formation of open-eyes in a gas stirred ladle. In the first model, water and silicon oils were employed to simulate liquid steel and slag respectively. In the second one, liquid Ga-In-Sn alloy was used to simulate liquid steel, while 12% hydrochloric acid simulated the top slag. The experimental results indicated that the gas flow rate, height of the lower liquid and height of the top liquid had a strong impact on the open-eye size. On the other hand, the viscosity of the top liquid and the interfacial tension between the two liquids had only little effect on the open-eye size. A semi-empirical model was developed to describe the size of open-eye as a function of the heights of the two liquids and the gas flow rate. The two sets of parameters obtained for the water and Ga-In-Sn models were very different. Industrial trials were also conducted to examine the applicability of the models. The model developed based on the Ga-In-Sn model could well predict the formation of an open-eye during ladle treatment. The model could be adopted by the industry to estimate the real gas flow rate by measuring the size of the open-eye online. On the other hand, the mathematical model based on water model experiments was unsatisfactory when applied to the industrial ladle process.