An experimental investigation of the boilover phenomenon for a liquid burning above a water sublayer indicates that boilover occurs when the boiling point temperature of a pure fuel is more than that of the water. In this situation, the fuel temperature near the fuel-water interface is somewhat limited by the presence of the boiling water and cannot reach the fuel boiling point. The boilover behavior of multicomponent fuels is similar to that of pure fuels. The temperature measurements at the onset of boilover for multicomponent fuels show that a fixed amount of superheat, 10K, exists in the water sublayer near the fuel-water interface. Onset time of water boiling was measured and compared with an estimated value that was derived by a simple analysis of unsteady conductive heat transfer.