Cargo tanks on oil tankers are loaded to 98% and in some cases 99% of capacity with the oil level well above the sea level. If the hull plating is breached, then due to the pressure of the oil on the ship bottom being greater than the pressure of the sea, oil will flow out causing pollution. When HBL method is used, the oil pressure on the ship bottom is equal to or less than that of the sea on the ship bottom. In this situation when the hull is breached, the sea flows in preventing pollution.