A vertical oil storage system is disclosed, having an oil tank for storing oil and water, an oil caisson coupled to the top of the oil tank, a water caisson coupled to the bottom of the oil tank, and a containment saucer at the interface between the oil and the water stored in the oil tank. Additionally, there is a water pipe extending from an upper water sump in the center well to the water caisson, a water passageway extending from the center well to the water caisson, and an oil pipe extending from the topside facility to the oil caisson.