Industrial processes usually work in multiple stages and require process analytical measurement technology to ensure safety, efficiency, and reliability of the processes. Among the various process analytical measurements (pH, conductivity, turbidity, etc.), the measurement and monitoring or control of oxygen also plays a central role in many pharmaceutical processes. Accurate and continuous measurement of the O2 concentration is crucial for safety and reliability in numerous manufacturing processes in the pharmaceutical industry. Oxygen analyzers based on TDL (tunable diode laser) spectroscopy are powerful and reliable in many applications that pose a real challenge for other technologies. The immunity to interference achieved through various precautions (e.g. filters or nitrogen purging), one-flange design with various process adaptations, the very low maintenance effort and the extremely fast response time make the METTLER TOLEDO GPRO500-TDL sensor a pioneer in gas analysis. The lecture will, among other things, examine the basics of oxygen measurement using TDL (Tunable Diode Laser) technology and present the various application examples in the various manufacturing processes in the pharmaceutical industry.