The quality of vegetable oils used in biofuel production is directly related to the quality of the final product. As metals play a significant role in vegetable oil oxidation and degradation, their presence is undesirable, even at low concentrations. The present study investigated how the presence of copper, in different oxidation states, copper(0) or copper(II), affects the stability of canola and sunflower oil, thus aiding in the understanding of oil oxidation mechanisms. Cupric oxide or metallic copper were added to the oil samples generating suspensions containing overall copper amounts equivalent to 2000 mg kg 1. The samples were maintained at 90 celsius degrees for fourteen days. Aliquots were taken periodically and evaluated with regard to oxidative stability, by determining the acid value, iodine value, by absorption UV Vis and Infrared (FT IR) spectroscopy, Raman spectroscopy and the Rancimat test. The results confirm that copper, no matter in what oxidation state, participates actively in vegetable oil degradation, suggesting that the metal species do not only influence the oxidation rate, but also the extent of the degradation processes. The FT IR spectra of samples derived from copper contaminated canola oil showed an increase in the (I2856/I1747)tx/(I2856/I1747)t0 ratio, i.e., a decrease of the ester groups. However, no changes in the bands with maximums at 1120 and 1098 cm 1 were observed, indicating that this metal acts as a catalyst in the hydrolysis process of ester bonds. Furthermore, the (I2856/I3009)tx/(I2856/I3009)t0 and (I2856/I3010)tx/(I2856/I3010)t0 ratios measured by FT IR spectroscopy, for canola and sunflower oil, respectively, and the (I2856/I3012)tx/(I2856 /I3012)t0 ratio measured by Raman spectroscopy showed a more pronounced increase in the copper containing samples. However, the results also suggest that olefinic bonds did not rupture during triglyceride oxidation, since, despite the fact that a decrease in the band related to cis C-H vibration was observed by both FT IR and Raman during the oxidation progress, no reductions in the iodine value were observed, indicating that the majority of the oxidation in the copper containing oils did not involve the loss of double bonds, but the isomerization of cis double bonds, directing the formation of products containing trans bonds. The results reported in this study indicate that copper in the (II) oxidation state exerts a greater catalytic effect than Cu in the form of metal particles, since the decrease in the induction time, as well as the increase in the production of secondary oxidation products, verified by measuring the absorption intensity at 270 nm, was more pronounced in samples contaminated with copper(II). The influence of a natural antioxidant, curcumin, on the oxidation stability of vegetable oils was also evaluated, and its addition to the oil samples containing copper(II) increased oil stability.