A very high resolution distributed optical-fiber temperature sensor system has been demonstrated using a time-resolved photon counting technique. The spatial resolution of the system is 3.5 cm. A temperature sensitivity of 2 degrees Celsius has been achieved with 1 minute integration time when averaging the data points over 10 cm. The system offers a practical solution for life assessment and monitoring of hot spots along the steam pipes in power plants.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.