An experimental study has been made on boilover phenomena in oil pool fires with water sublayer. The objective of this research effort is to improve our understanding for physical characteristics of the boilover process, and to explore a new way for detecting and predicting the occurrence of boilover. The fire behavior of boilover process is examined for different oil types. Local temperature histories of oil-water sublayers during the burning progress are measured. The characteristics of combustion noise to boilover process are analyzed in time and frequency domains.