The liquid depth sensing and identification system determines both the pressure head or depth, and therefore the quantity, of a liquid in a tank, as well as determining the characteristics of the liquid at the bottom of the probe. Two principles of operation are disclosed herein. The system may use a gas bubble collector about the outlet end of the purge tube, with the difference in height of the collector and purge tube mouths defining the very small difference in pressure head required to resolve the bubble emission characteristics produced in different liquids. Alternatively, the system incorporates a mass flow sensor capable of detecting minute changes in mass flow as bubbles are emitted from the purge tube in order to determine the type and characteristics of the liquid. The system operates using an open loop principle of operation, with no feedback provided to control the purge pump.