An experimental study of boilover phenomena in oil-tank fires supported on water has been performed. It is found that a typical process of liquid fuel burning on water consists of three basic stages: a quasi-steady period, a boilover premonitory period and a boilover period. Basic characteristics during the boilover process such as the flame structure, the fuel burning aspects, and the thermal structure of the oil-water layer at each stage have been examined. In particular, phenomena such as water seething at the oil-water interface and combustion micro-explosion noise emission, which appear only in the boilover premonitory period, have been examined and analysed in detail. By correlative analysis of these sub-processes, it can be concluded that boilover premonitory noise is certainly emitted before the occurrence of boilover and is quite closely connected with the temperature distribution of the oil-water layer before boilover occurs. This conclusion is helpful in understanding the mechanisms of boilover phenomena and offers a practical means to predict the occurrence of boilover.