This project has two general objectives: 1) determine the potential of supercritical CO2 extraction to extract a unique fresh onion flavor, and 2) determine the feasibility of supercritical extraction in the process of onion flavor extraction, including methods of process optimization. A fresh onion flavor has been extracted using supercritical CO2 extraction. The flavor has been shown to be unique by means of a trained taste panel and through GC-MS analysis of the SC-C02 extract compared to traditional commercially distilled onion oil flavor. Techniques to improve the efficiency of the extraction process has included the use of entrainers in the C02 solvent, reverse osmosis concentration of onion juice feed prior to extraction, and adsorption onto resins followed by SC-C02 desorption. Each of these techniques have demonstrated an increase in SC-C02 extraction efficiency. Mass spectrometry has provided the critical component of evaluation of the composition or quality of the onion oil extract resulting from the various techniques of processing. This includes a comparison of types of compounds present in each extract as well as a secondary method of relative quantification of material.