The objective of this work was to investigate the catalytic wet air oxidation of p-coumaric acid, a biorecalcitrant phenolic compound typically found in olive oil wastewaters in the presence of Pt and Ru supported catalysts. The influence of the operating variables were established. The most important intermediates determined by HPLC measurements suggest a rapid attack by oxygen of the side-chain of p-coumaric acid, and the mineralization proceeds through different aromatic compounds reacting further to aliphatic intermediates (mainly acids). Important mineralization yields were achieved in the presence of the catalysts at 140 degrees C and 50 bar air. The importance of the nature of the support (TiO2, ZrO2) on the adsorption of p-coumaric acid was demonstrated. (c) 2005 Elsevier B.V. All rights reserved.