Olive oil occupies a unique position among edible oils due to its chemical composition and its beneficial effect on health. Because of this, it is more expensive than other vegetable oils and it is a potential target for adulteration. Determination of triacylglycerol composition by liquid chromatography is particularly useful for detecting the presence of small amounts of other vegetable oils in olive oil. The theoretical content of triacylglycerol is calculated on the basis of the fatty acid composition determined by gas chromatography. Using the experimental and theoretical data of the triacylglycerol composition, the computer program, which is constituent part of the method, gives an answer whether the oil is genuine or non genuine. For this study we used Dalmatian extra virgin olive oil, vegetable oil and their mixtures. The method, although still in development, have a detection level 1% for vegetable oil.