Under certain circumstances, the water on which a burning pool of liquid fuel is supported may begin to boil. The water vapor that is released and escapes through the fuel surface tends to atomize the oil, which results in an emulsive-droplet flame above the fuel surface. This phenomenon, called boilover, has been observed for large scale pool fires, but the mechanism causing it to occur has not been fully investigated yet. This paper describes fundamental aspects of the effect of a boiling water sublayer on the behavior of pool fires.