Homogeneously and heterogeneously base-catalyzed sunflower oil methanolysis was investigated without and with the presence of the cosolvents. In the former case, KOH and tetrahydrofuran (THF) were used as a catalyst and a cosolvent, respectively, and the reaction was performed at the reaction temperature of 10 degrees C and the methanol-to-oil molar ratio of 6:1. In the latter case, CaO and various organic solvents such as THF, n-hexane, dioxane, diethyl ether, triethanolamine, ethyl acetate and methyl ethyl ketone were employed as a solid catalyst and a cosolvent, respectively, and the reaction was carried out at the reaction temperature of 60 degrees C and the methanol-to-oil molar ratio of 6:1. The rate of KOH-catalyzed sunflower oil methanolysis increased with increasing the THF concentration up to 50% of the oil mass, which was due to the self-enhancement of the interfacial area as the result of decreasing the mean drop size. No effect of THF present at the concentration of 20% on the rate of CaO-catalyzed methanolysis was observed, but at higher THF concentrations, the reaction was delayed and the final fatty acid methyl esters (FAME) yield was decreased. Of all tested cosolvents, only n-hexane and THF slightly improved the methanolysis reaction in its initial period, triethanolamine and ethyl acetate had no effect, while diethyl ether, dioxane and methyl ethyl ketone negatively influenced the reaction rate and the FAME yield. (c) 2012 Elsevier Ltd. All rights reserved.