The transesterification experiments were performed in conical flasks using 250 g of used frying oil prepared as above. The ester preparation involved a two-step transesterification reaction [7]. The two-step reaction utilized 2.5 g (1% by weight of the oil) of potassium hydroxide (powder) or 1.25 g (0.5% by weight of oil) of sodium hydroxide as catalysts. The catalyst was first dissolved in 72 g of ethanol (6:1 molar ratio of anhydrous ethanol to oil), which represented a 100% excess of the stoichiometric amount required for the transesterification. The required amount of catalyst was quickly weighed, protecting it as much as possible from atmospheric moisture and carbon dioxide. The solid catalysts were dried using microwave oven for 1 min at high power (output power, 750 Watts). Dryness is absolutely essential as any water in the system will consume some of the catalyst and slow the transesterification reaction. The solid catalyst was added to the ethanol and was vigorously stirred with slight heating until completely dissolved. The ethanol and dissolved catalyst were then added to the oil and was stirred vigorously. Reaction was performed at room temperature. Six sets of the reaction mixtures were prepared and allowed react for 3, 15, 30, 45, 60 and 75 min respectively. The reaction was arrested in each sample by adding ten to fifteen drops of water. The reaction mixture was poured into a separatory funnel; the top ester layer was poured into another flask and transesterified a second time using the same method as the first reaction.