This Small Business Innovation Research Phase I project proposes to develop a highly-multiplexed high-temperature sensor system to enable distributed temperature and pressure measurements for reservoir management in geothermal wells. The proposed system synergistically leverages recent advances in laser fabrication of in-line fiber interferometers with state-of-the-art high- resolution optical time domain reflectometers. The resulting system will withstand temperatures up to 800 degrees C and will be insensitive to hydrogen-induced spectral attenuation shifts that render Raman spectroscopy methods inaccurate.<br/><br/>The commercial application of this project is in the management of energy producing geothermal wells. Electricity generated from these wells has the potential to fill a significant portion of the country's demand for energy. However, costs must be lowered to make geothermal energy economically competitive with fossil fuel energy. Improved geothermal reservoir management is expected to lead to lower energy cost, but requires down-hole instrumentation that can survive the harsh environment.