To provide a method for storing an oil containing a sublimable substance in a tank having a gaseous phase vent device near its ceiling, whereby the vent device is prevented from being closed with the sublimable substance and hence an excellent effect such as storing the oil safely for a long time is exhibited.

The oil is stored while a layer of a liquid smaller in specific gravity than the oil and incompatible with the oil is formed on the surface of the oil. Naphthalene or the like may be used as the sublimable substance. A heavy oil may be used as the oil. Water may be used as the liquid smaller in specific gravity than the oil and incompatible with the oil. It is preferable that the thickness of the layer of the liquid is 10 to 50 cm. When the layer is too thin, this layer may be cut. When the layer is too thick, on the other hand, the effective capacity of the tank decreases.