Abstract: The temperature of oils stored in a tank decreases with time, with temperature drop being a function of time and heat conduction. Temperature drop of the oils is sometimes required to be within a limited range during storage and transportation. Taking vertical dome tank as an example, the calculation formula for insulation thickness of oil tank are given based on controlled temperature drop and duration. When insulation thickness is given, these formula can be used to determine oil temperature drop in a certain duration, or the duration required to decrease the oil tem-peraure to an allowable level.