Purification of waste cooking oils (palm oil and soybean oil) using supercritical carbon dioxide (scCO2) extraction has been investigated. The purified oils were characterized by their acid value, conjugated diene value, total polar compound measurements, and high-performance size exclusion chromatography. Using optimal extractions conditions of 353.15K, 20MPa, and CO2 flow rate of 40g/min, 80% of the oil was recovered and the purified oil compositions and properties were very close to those of the fresh oils. At higher pressures or lower temperatures, the separation efficiency of the scCO2 extraction was significantly reduced.