In this study, Oleum hyperici (St. John's Wort oil) was investigated according to its oxidative stability and antioxidant activity parameters. A homemade and two different brands of oils were used for comparative reasons. Oxidation process regarding kinetics and thermodynamics studies achieved by accelerated Rancimat conditions (100-140 °C). The quality parameters of the oil samples were compared depending on phenolic and flavonoid contents, antioxidant activity, free fatty acid quantity and shelf-life. Principal component analysis (PCA) has been also applied to comprehend the relationship between these three groups and their quality parameters. The homemade oil has been predicted to have almost twice longer shelf-life than that of the commercial ones (119 days versus 66/69 days). Additionally, lipid oxidation in the St. John's Wort oils has been found to be endothermic and non-spontaneous depending on the thermodynamic indexes.