Accurate and reliable measurements of contaminants in Ethylene feedstocks from steam crackers have historically required time-consuming and higher maintenance methods such as ion mobility spectroscopy (IMS) or chromatography (GC). A near real-time analysis allows better control of the hydrogenation process to minimize contaminants such as acetylene (C2H2), ammonia (NH3) and water (H2O) that will poison catalysts in further chemical processes. This paper reports on the design, development, and deployment of novel instrumentation, consisting of innovative laser-based gas analyzers for rapid measurements of multiple contaminants with extremely high sensitivity, accuracy and dynamic range. This new instrumentation, based on a Cavity-Enhanced Laser Absorption Spectroscopy technique, can use advanced calibration techniques to directly measure without any scrubber or elution technique. This enables continuous measurements with 1-second time resolution and thus provides a means for process monitoring and control, including tracking upsets far above the typical limits.