Alkali-catalyzed transesterification of waste cooking oils, collected within Ho Chi Minh City, Vietnam, with methanol was carried out in a laboratory scale reactor. The effects of methanol/waste cooking oils ratio, potassium hydroxide concentration and temperature on the biodiesel conversion were investigated. Biodiesel yield of 88-90% was obtained at the methanol/oil ratios of 7:1-8:1, temperatures of 30-50 degrees C and 0.75 wt% KOH. Biodiesel and its blends with diesel were characterized for their physical properties referring to a substitute for diesel fuel. The results showed that the biodiesel experienced a higher but much narrower boiling range than conventional diesel. Carbon residue content was up to 4 wt%. Blends with a percentage of the biodiesel below 30 vol% had their physical properties within EN14214 standard, which indicated that these could be used in engines without a major modification. Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.