A spectroscopic analyzer has been developed for rapid, accurate quantification of acetylene and methyl acetylene in hydrocarbon cracked gas processing plants. The system utilizes off-axis integrated output cavity spectroscopy to measure the near-infrared, cavity-enhanced absorption spectrum of ethylene, methyl acetylene, and acetylene and employs a chemometric data analysis strategy to quantify the respective constituents. Initial tests verified that the instrument is capable of measuring, <0.050 ppmv of acetylene, has a precision of +/-0.025 ppmv, and can accurately determine acetylene concentrations with comparable accuracy to a gas chromatograph (+/-0.1 ppmv) in an actual process stream composition matrix under plant operating conditions. Subsequently, the prototype analyzer was installed in a hydrocarbon facility for field-trials, where its rapid response (< or =30 seconds or better) allowed it to measure transient acetylene and methyl acetylene fluctuations that were too fast for conventional methodologies. Moreover, the analyzer showed an extended dynamic range that enabled measurement of very high acetylene levels (0-1000 ppmv) during abnormal plant operations. Finally, two commercial acetylene analyzer systems with stream-switching capabilities were implemented in an industrial facility and initial results are presented.