In tropical and subtropical countries, utilization of unprocessed plant oil or used frying oil as household cooking fuel promises to be a competitive alternative to well known fuels like wood and kerosene. However, the use of unprocessed plant oil in plant oil pressure stoves leads to the formation of deposits inside the vaporizer, which have to be removed from time to assure a proper operation of the plant oil pressure stove. Therefore, the objective of this study was to investigate the effect of free fatty acid content of coconut oil on performance and deposit formation in plant oil pressure stoves. Test fuels with different levels of free fatty acid content were prepared by aerating the coconut oil with dry air (5.04 l O(2)/kg h) at a temperature of 85 degrees C. Experiments were performed with the plant oil pressure stove 'Protos' (BSH Bosch und Siemens Hausgerate GmbH). As a result, 0.15 g of deposits per kg of consumed oil was found for fresh coconut oil with free fatty acid content of 0.03%, which served as control. Aged oil with a free fatty acid content of 23.1% resulted in 6.48 g deposits per kg of consumed test fuel. Conradson carbon residue CCR of 0.18% was low for control and increased to 0.82% for aged oil. Specific fuel consumption was in a range between 0.284 and 0.304 kg/h without significant differences between the fuels. Performance of the plant oil pressure stove was not affected by the amount of free fatty acids in the plant oil. However, lower heating value decreased from initial 35 MJ/kg for control to 30 MJ/kg for aged fuel, and as consequence power output from plant oil pressure stove decreased. Therefore, plant oils with free fatty acid content below 5%, which is equivalent to an acid value of 10 mg KOH/g, are recommended as fuels for plant oil pressure stoves. (C) 2009 Elsevier Ltd. All rights reserved.