Stearic acid (C17H35COOH: C-17-acid) was treated using a batch reactor with supercritical water (SCW) of 673 K and 0.17 g/cm(3\) for 30 min. In SCW, C-17-acid was stable (2% conversion) and the main products were CO2 and C-16 alkene. An addition of alkali hydroxide (NaOH and KOH) in the SCW reaction enhanced the decarboxylation of C-17-acid with the main products being CO2 and C-17 alkane. Metal oxides (CeO2, Y2O3 and ZrO2) enhanced the decarboxylation of C-17-acid and the main products were C02 and C16 alkene. Based on the results, the reaction mechanism was proposed. (c) 2006 Elsevier Ltd. All rights reserved.