Disposal of waste palm cooking oil (WPCO) via an environmental-friendly route is of major importance in the quest for sustainable development. In this study. WPCO was utilized instead of refined vegetable oils as the source of triglycerides for biodiesel production. WPCO contains several impurities, such as water and free fatty acids, which limit its application in catalytic transesterification processes. Consequently, a catalyst-free process using supercritical methanol was employed to investigate the potential of WPCO as an economical feedstock for biodiesel production. The parameters that influence the reaction, including reaction time, temperature and the molar ratio of alcohol to oil, were investigated. For comparison purposes, refined palm oil (RPO) was also subjected to supercritical methanol reaction and it was found that both processes produced comparable optimum yields of 80% at their respective optimum conditions. Hence, it can be concluded that WPCO has high potential as an economical and practical future source of biodiesel. (C) 2010 Elsevier Ltd. All rights reserved.