Distributed Temperature Sensor (DTS) technology uses fiber-optic cable to measure a continuous temperature profile along the wellbore. Compared to conventional production logging tools (PLT), DTS can provide operators real-time well information without intervention. Applications, from flow profiling to gas lift surveillance, have grown steadily in recently years. DTS applications require reliable data modeling and analysis or measurement interpretation. The complexity of the data analysis has been a barrier to DTS usage. This paper presents software tools developed for DTS interpretation. The model behind the software is based on steady-state energy balance, and it is applicable for gas and oil wells in both onshore and offshore environments. The software allows users to run in two modes: forward simulation and flow profiling. The forward simulation mode calculates the temperature distribution along the wellbore for any given production profile, and this mode is critical for the model calibration. It is also very useful for emulating "what-if" scenarios, such as forecast and gas lift surveillance. The flow profiling estimates the production profile based on measured temperatures, which is the basis for the real-time well monitoring. The model is tested against other models and good agreement has been obtained. This paper presents two examples: result comparison against TIPP, a computer program package developed by Chevron Corp, and a field example to verify gas lift valve operation. Introduction DTS is the name of the class of instruments that measure temperature continuously through the optic fiber installed along the entire wellbore length. DTS most commonly operates on the same principles as an Optical Time-Domain Reflectometer (OTDR). It uses physical phenomena such as Raman scattering, which transduces temperature into an optical signal. Laser light pulses are generated by the DTS instrument (DTS box) and launched down the fiber sensor. As laser pulses travel down, a portion of the light is scattered away. The light that is scattered back towards the source (DTS box) is called backscatter. Raman backscatter is caused by molecular vibration in the fiber, resulting in the emission of photons, which are shifted in wavelength from the incident light.1 Positively shifted Stokes backscatter is temperature independent, while the negatively shifted Anti-Stokes Raman backscatter is temperature dependent. The intensity ratio of Stokes/Anti-Stokes is used to calculate temperature. Since pulses become weaker after the scattering loss, the calculated temperature accuracy depends on calibration and fiber loss stability.