Base-catalyzed transesterification of waste cooking oil for the production of biodiesel was assisted by the addition of cosolventTetrahydrofuran (THF). In addition to lowering of reaction temperature and reduction in reaction time for transesterification, THF facilitated production of methyl ester in a single phase. THF-assisted base-catalyzed reaction was optimized for various parameters. Maximum biodiesel production(92.8%) was obtained with 4% THF; 0.6% sodium methoxide (catalyst), 6:1 methanol to oil ratio, 45 min reaction time, 50 0 C reaction temperature. Added to this, maximum glycerol recovery (18.62%) was obtained at 50 0 C using lower concentrations of THF(2%). Use of THF highlights even more economically viable and greener potential for biodiesel production as this co-solvent is non-toxic, unreactive and of biomass origin.