Various experimental studies on effect of ventilation on behaviour of fire in compartment are available in literature. Recently, experiments have been conducted to study fire behaviour in compartment with more than one ventilation opening located on opposite walls (Kumar and Naveen, 2007). Two different fuels (benzene and kerosene) are burned in three trays of different size in compartment with single ventilation opening as well as in compartment with two ventilation openings placed on opposite walls (in cross-condition). These results have been used to show how CALTREE (Kumar, 2004), a simple pre-flashover mathematical model to predict temperatures in compartment with single ventilation opening, can be used to predict behaviour of fire in the compartment with cross-ventilation condition. The two methods: equivalent area methods and gas flow methods have been discussed. In the first method there is no need to modify the model developed for the compartment with single ventilation opening. It is found that both the methods give same results in the present study.