AbstractTriolein was heated at 190°C (375°F) in a deep‐fat fryer for 12 h/day until high‐performance size‐exclusion chromatography indicated polymer formation had exceeded 20%. Increases in the free fatty acid, total acid value, food oil sensor andp‐anisidine values upon heating indicated that thermal oxidation and degradation of triolein had occurred. After the initial sample (day 0), the peroxide values decreased to very low values. The amount of polymeric triacylglycerol material increased during heating. Linear regression analysis of percent polymer vs. heating time indicated that the sample would contain ≥20% polymers after 51.1 h of heating. Capillary supercritical fluid chromatography (SFC) was used to determine the percentage of triolein remaining after 12, 24, 36, 48 and 60 h of heating, which was 68.6, 53.9, 35.9, 33.0 and 19.0%, respectively. The average reaction rate constant (apparent first‐order) for the change in triolein concentration, SFC, during heating was 0.0256±0.0011 h−1.