The primary objective was to study the purification of an oily wastewater from a lubricant production unit using ultraviolet irradiation and hydrogen peroxide. The influence of hydrogen peroxide concentration, initial pH of the solution and of the addition of ferric ions on the chemical oxygen demand (COD) was examined. In each case, the concentration of the compounds contained in the oily wastewater was determined. It was shown that a 20-45% COD removal was achieved with 830-1660 mg 1(-1) H2O2. Gas chromatography-mass spectrometry analysis showed that the organic compounds of the wastewater decomposed to organic acids that were very resistant to photo-oxidation. Among these compounds, ethylene glycol remained almost unchanged by the attack from hydroxyl radicals. Acidic pH and Fe(III) addition enhanced significantly the photo-oxidation of the wastewater. (C) 2003 Elsevier Science B.V. All rights reserved.