The program for calculation of gasoline inventory in an oil depot is a tool for calculating quantity of gasoline for API ranging from 50 to 85. This developed program written in Delphi languages. Furthermore developed program extend effective calculate cover quantity of fuel oil for API ranging from 0 to 50 and it can calculate value API gravity at 600F. To operate the developed program, data of oil level, temperature of oil in tank, API and temperature as read value from hydrometer or use value API at 600F could be input by users. Results from comparison between developed program has value equal that of another program if the effect of expansion or contraction of tank from temperature of oil not considering. But if effect of temperature of oil is condition for consider the results of developed grogram will be correct value more than another program. According to calibration tank of Thailand use temperature at 860F for calculation oil quantity so the calculation by consider effect of temperature of oil will be correct values.