TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The reaction mixture is heated to 45-120degreesC for at least 0.5 hours. Preferred Component: The metal oxide or metal complex is a dialkyl tin oxide (where alkyl groups in the dialkyl tin oxide are 2-4C alkyl groups). The triglyceride further comprises free fatty acids (1-99%).    TECHNOLOGY FOCUS - POLYMERS - Preferred Component: The ion exchange resin has sulfonic acid functionality. EXAMPLE - In a three-necked flask (containing 75 g activated molecular sieves 3A), was added a mixture consisting of corn oil (104.8 g), stearic acid (5.79 g; 5.2% of oil and stearic acid), Amberlyst 45 (RTM: ion exchange resin) (6.0 g), dibutyl tin oxide (DBTO) (5.9 g) and methanol (303.0 g). The mixture was allowed to reach reflux temperature ( approximately 64degreesC) with rigorous stirring (250 rpm). Initially, the mixture developed foam which subsided after refluxing for 1 hour. The process was carried out at 64-65degreesC (reflux temperature) and atmospheric pressure for 3 hours. At this point, sample ( approximately 8 ml) was removed, which after filtering the solid catalyst, separated into two phases, a methanolic phase on top containing a mixture of methyl esters of fatty acid and a bottom phase of mainly unreacted corn oil. After 11 hours, the mixture was cooled to ambient temperature. The mixture consisted of a single liquid phase. The ion exchange catalyst was recovered by filtration from the organic phase. After the filtration step, the methanol was evaporated resulted in residual oils (115 g). Again, the residue consists of one phase only incorporating in it the glycerol and the tin catalyst. The addition of water (27.4 g) formed a precipitate (presumably the tin catalyst and glycerol). The solid was centrifuged resulting in two phases only, which was added to the organic phase and white paste (12.3 g), presumably a mixture of the tin catalyst together with glycerol. The organic phase was washed again with brine solution (54 g), dried over magnesium sulfate anhydrous and after gravity filtration the solvent was evaporated resulting in biodiesel fuel (89.5 g).