Mixing of fresh olive oil with olive oil from previous season is an emerging problem, and several chemical parameters have been proposed for the determination of this type of adulteration. The main objective of this study is to investigate the changes in several quality parameters (fatty acid alkyl esters, diacylglycerols and pigments) and spectral profiles of olive oils and olive oils adulterated with old olive oil as quality and authenticity indicators. For this purpose, fresh olive oil samples from North and South Aegean Regions and their blends with olive oil from previous year were stored for 15 months and changes in basic quality parameters (free fatty acidity, specific absorbances, fatty acids), fatty acid alkyl esters, diacylglycerol and pigment contents as well as ultraviolet-violet visible and mid-infrared spectral data were assessed to investigate effect of storage. Data were examined using multivariate analysis. Free fatty acid limit of extra-virgin olive oils was exceeded in 6 months for the samples mixed with old oil at concentrations of 30% and higher. The most significant changes during storage were observed in free fatty acidity, fatty acid alkyl ester and pigment composition of the olive oils. Spectral data and pigment composition provided the best separation with respect to storage periods. None of the parameters investigated provided clear results in terms of detection of adulteration.