US Patent 7197407 Fuel tank level monitoring system and method

A method and system for monitoring a level of liquid fuel in a tank having a known capacity, wherein the tank fluidly communicates with a fuel supply line through which the fuel is delivered in gaseous form. The method comprises measuring a flow rate of gaseous fuel flowing through the supply line, calculating an expended fuel volume based on the measured flow rate, and determining a remaining liquid fuel level in the tank based on the expended fuel volume and tank capacity. A delivery of liquid fuel to the tank is prompted in response to the remaining liquid fuel level.