Advanced Technologies Group, Inc. proposes the development of a Liquid-Oxygen Mass Gauge, (LMG) for In-Space cryogenic storage capable of continuous monitoring of liquid quantities to better than 1% accuracy. The proposed sensor builds on previous liquid hydrogen sensor development successes and patents. It can be utilized to measure cryogenic propellants, and sub-critical cryogenic fluids in use on a wide range of space applications and in ground applications to monitor fluids ranging from liquid oxygen to MMH and N2O4. The LMG can also indicate the presence of contaminants such as nitrogen used to purge the system. The current methods use either wire resistance measurements, capacitance or point sensors, combined with pressure and temperature measurements. The LMG will be lighter, require less energy to operate, and provide less heat leak than existing technologies. Current techniques will not function correctly in boiling or stratified liquid cryogens or in reduced gravity. During phase I, Proof-of Concept experiments will be performed with liquid oxygen. Commercial applications in the home health care industry have been identified.