Sebacic and azelaic acids, which are representative of high molecular weight dicarboxylic acids, were oxidized in a batch reactor with H2O2 oxidant in water from 300 degrees C to 400 degrees C at sub- and supercritical conditions. Intermediate products were identified based on GC-MS, HPLC, and H-1 NMR. The main oxidation products were dicarboxylic acids and the minor products were monocarboxylic acids. (omega-1)-Keto acids, aldehyde-acids, and gamma-lactones with carboxylic groups also were identified. On the basis of the products identified, the oxidation pathways of high molecular weight dicarboxylic acids were formulated. The oxidation of high molecular weight dicarboxylic acids proceed with the consecutive oxidation of higher to lower molecular weight dicarboxylic acids mainly through the oxidation at alpha-, beta-, and gamma-carbons to a-COOH group. The oxidation of dicarboxylic acids was also accompanied by oxidative decarboxylation, leading to the formation of monocarboxylic acids. (C) 2007 Elsevier B.V. All rights reserved.