The OSI of the frying oils decreased exponentially during the frying process. The slope of the linear equation obtained from the plotting of the logarithms of OSIs versus frying times, which was considered to be a measure of the rate of OSI decrease during the frying process, was significantly different for the oils. The results of the present study confirmed that the OSI determined via the Rancimat test on the original oil can not guarantee or predict the actual frying performance of the oil but it is considered that this method can be useful to act as a “screening” test and eliminate the possibility of introducing lower stability oils into the production area with all the attendant consequences. There was a strong correlation (r2 = 0.9949) between the OSI and TPC of the frying oils (y = 51.01 x-0.9726). Assuming that 24% of TPC is the maximum level permitted in frying oils, the OSI of a used frying oil should be ≥ 2.32 h. There was a power relationship (y = 120.9 x-1.0423) between the OSI and CV with a high determination coefficient (r2 = 0.9856). Assuming that 50 µmol/g of CV is the maximum level permitted in frying oils, the OSI of a used frying oil should be ≥ 2.05.

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