A method and system of dispensing a fuel from a fuel tank to a recipient fuel tank. The method includes scanning a tag by a scanner from a smart device, wherein the smart device also comprises a communications processor, recording an initial inventory level of the fuel in the fuel tank, estimating a density of the fuel, opening a valve to dispense a predetermined amount of the fuel, and recording a final inventory level after the dispensing the fuel, upon estimating that the density of the fuel is within a predetermined range, and shutting the valve and communicating to relevant personnel about the difference in fuel density, upon estimating that the density is outside of the predetermined range.