Phenolic compounds in Greek olive oils were analyzed by reverse phase high performance liquid chromatography (RP-HPLC) with diode array detector (DAD) and by GC–MS after extraction with methanol:water 80:20 and derivatization with bis (trimethylsilyl) trifluoracetamide and trimethylchlorosilane (BSTFA:TMCS 99:1). Tyrosol, hydroxytyrosol and the decarbomethoxy ligstroside and oleuropein aglycons in the dialdehydic forms were the most abundant compounds. 3,4 dihydroxyphenylacetaldehyde, syringaldehyde, the cis form of ferulic acid, phydroxybenzoic acid, caffeic acid and luteolin were identified. Phenolic compounds, mainly polyphenols are bioactive compounds in virgin olive oil and they have been related to the stability of the oil. Several reports mention natural antioxidants such as polyphenols in olive oil for their antivascular and antimicrobial effect on human health. Total phenolics were also determined by the Folin-Ciocalteu colorimetric method. Fatty acids in the examined samples were determined by gas chromatography (GC) with FID detection.