Olive oil residues were tested for their composition in simple phenolic compounds as a function of the extraction system, i.e. the three- and two-phase centrifugation systems. Phenolic compound extraction with ethyl acetate was efficient and allowed recovery of 28.8 and 42.2% of total phenols present in dry olive oil residues originating from three-phase and two-phase systems, respectively. The qualitative and quantitative HPLC analyses of the extracts showed that hydroxytyrosol and p-tyrosol were the most abundant phenolic compounds. p-coumaric, caffeic, ferulic and vanillic acids were also present. The phenolic extract from the two-phase system had the highest concentration in hydroxytyrosol (1.16% (w/w) dry residue) and the strongest antioxidant activity. Olive oil residues were confirmed as a cheap source of large amounts of natural phenolic antioxidants.