The high temperature, high pressure wet oxidation reaction of quinoline has been studied as a function of initial concentration, pH and temperature. At neutral to acidic pH, it is effective in the oxidation of quinoline at 240 degrees C and above, whereas under alkaline conditions the reaction is markedly slowed down. The results indicate that the reaction is an auto-catalysed, free radical chain reaction transforming 99% of quinoline to other substances. Of the quinoline. 30-50% was oxidised to CO2 and H2O depending on the initial concentration. Wet oxidation of deuterium-labelled quinoline was used as a method for verifying and quantifying the reaction products. Fifteen reaction products were identified and quantitatively determined. accounting for 70% of the carbon present after treatment, Nicotinic acid was a main product, accounting for up to 35% of the parent substance, The formation of succinic acid is suggested to be a result of a coupling reaction of the acetic acid radical A reaction mechanism is suggested for the degradation of quinoline: it involves hydroxyl radicals and the possible interaction with autoclave walls is discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.