A Simulation of oil loss in storage tank, written in Visual Basic language, is developed in this work. This simulation is a tool for calculating typical oil loss from three types of tank with true vapor pressure ranging from 6 to 10 psia, in normal working condition. Categories of tank considered here are internal floating roof tank, external floating roof tank, and fixed roof tank with diameter of 20 to 120 feet. To operate the simulation program, data of average temperature, wind speed, tank characteristics, product characteristics and throughput volume could be input by users or retrieved from a database prepared previously. Graphical comparison between loss from the developed program and that from another program indicates that the estimation of the developed program is higher than that of another program but becomes closer to the data reported presently. This improvement is due to consideration of many parameters having influences on evaporation loss of oil in the storage.