The production of biodiesel fuel from crude roselle oil was evaluated in this study. The process of alkali-catalyzed transesterification with methanol was carried out to examine the effects of reaction variables on the formation of methyl ester: variables which included methanol-to-oil molar ratios of 4: 1-10: 1, catalyst concentrations of 0.25-2.0% w/w of oil, reaction temperatures of 32-60 degrees C, and reaction times of 5-80 min. The methyl ester content from each reaction condition was analyzed by gas chromatography (GC), the optimum condition having been achieved at a methanol-to-oil molar ratio of 8: 1, a catalyst concentration of 1.5% w/w of oil, a reaction temperature of 60 degrees C, and a reaction time of 60 min. The resultant methyl ester content of 99.4% w/w, plus all of the other measured properties of the roselle biodiesel, met the Thai biodiesel (B100) specifications and international standards EN 14214: 2008 (E) and ASTM D 6751-07b, with the exception of a higher carbon residue and lower oxidation stability. (C) 2009 Elsevier Ltd. All rights reserved.