Makel Engineering, Inc. proposes to develop a miniaturized Multi-Species Chemical Microsensor Instrument suitable for real-time, in situ measurements of hydrogen, oxygen, water vapor and mixture thermal conductivity for monitoring purge effectiveness in cryogenic propellant lines. Helium is a scarce, strategic and non-renewable natural resource. NASA is a major user of helium and significant future cost savings in operations can be realized with improved monitoring of purge activities. Without real time measurement of species being purged from systems, extended purge cycles and excess helium is used to ensure completely purged lines. The proposed sensor system will incorporate the required microsensors in a compact probe to enable multi-parameter monitoring in a single measurement port. The system will be designed to be permanently installed in purge and vent lines at cryogenic propellant storage, transfer, test stand and launch facilities. This program will adapt low cost and low power chemical microsensor technology which was originally developed for leak detection applications and recently been demonstrated in proof of concept cryogenic vent tests at NASA to develop a low cost, robust integrated sensor probe and electronics with data interfaces suitable for real time monitoring and control helium purge sequences to minimize overall helium usage.