Many fire accidents in engine rooms of ships and marine structures come into existence in the world, and the unexpected burning of hydrocarbon liquid, such as fuel oil and lubrication oil, tends to be a good half of those primary cause. For the preventive design of oil burning fire in engine rooms, it is necessary to be grasped entirely the oil pool fires phenomena by an analysis taking thoroughly account of the governing factors and the characteristics of flammability liquid fire In order to investigate the distinctive factors of fire spread and extinguishing by some numerical simulations of fire accident in an engine room, the basic experiments on oil burning are executed in the condition of (1)oxygen rich atmosphere, and (2)oxygen lean atmosphere. Furthermore, the oil burning phenomena in enclosed-compartment is estimated qualitatively using a simplified mathematical model with a principle feature of enclosure fire. From the results of these experiments, it can be clarified as for threshold conditions of fire spreading, thermal properties and states of oil pool fires.