Abstract: A container for containing therein contents that develop a vapor pressure. The container has a cover provided with a vent opening for relieving internal pressures in the container when a predetermined internal pressure is exceeded. Control of the excess pressure venting is provided by a deformable seal that provides a pressure-tight seal between the cover and the container. The seal normally closes the vent opening and is deformable outwardly through a lateral opening on a peripheral flange on the cover when internal pressure in the container exceeds a predetermined limit excess pressure. The vent opening is disposed on the top of the cover so that as the seal deforms outwardly it uncovers the vent opening to relieve excess pressure. The material from which the seal is made is flexible and deformable and has memory so that it restores itself to a position closing the vent opening when the excess pressure is relieved.