Abstract: The present invention relates to a process and device for measuring the level and the specific gravity of a liquid e.g. liquified methane, contained in large-capacity tanks.The installation comprises two hydrostatic probes for spray a neutral gas into the tank, the first probe emerging near the bottom of the tank and the second slightly below the maximum filling level, a pressure differential/electric voltage transducer each of whose two inputs is connected to a hydrostatic probe, a system for numerically displaying the level and the specific gravity of the liquid contained in the tank, at least one pick-up capable of transmitting a signal when the liquid reaches the predetermined level in the tank, and a device for adjusting the value of the specific gravity of the liquid when the liquid reaches the predetermined level in the tank.