TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The catalyst is a metal oxide, metal hydroxide (preferably sodium hydroxide, and/or potassium hydroxide) and/or metal carbonate.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The method involves flowing the first fluid comprising an alcohol and a second fluid comprising an oil to the microreactor. The method further involves using a catalyst to produce the biodiesel. The method additionally involves blending the biodiesel produced by the method with petroleum-based products (greater than zero wt.% to less than 100 wt.%). The method involves transesterification process, and the temperature at which the transesterification reaction is conducted is 25-350 (preferably 25 to less than 250 degrees C). The method is performed at supercritical conditions, where the alcohol is supercritical. The method involves providing alcohol-to-triglycerides in a molar ratio of 3:1. The method involves providing several microreactors. The oil and alcohol fluid layers have fluid layer thicknesses in the microreactor of 10-500 microns. The surface-to-volume ratio of microchannels is of 10000-50000 m2/m3. The microreactor has several laminae with at least one lamina defining at least one microchannel for receiving fluid. The microreactor includes at least one manifold for distributing fluid flow to individual microchannels. The oil and alcohol fluids are pumped to the microreactor using a pump volume flow rate ratio of 3:4. The oil and alcohol fluid is used at a molar concentration of 1:7.2. The method further involves separating two phases produced by the reaction, by distillation process, and/or centrifugation process. The oil conversion to biodiesel increases with increasing mean microreactor residence time. The metal hydroxide as catalyst is used in 1.0 wt.% of the soybean oil used for the transesterification reaction. The method involves using a microchannel having a 100 microns thickness. The conversion of soybean oil to biodiesel is of 12% at 0.4 minute mean residence times (MRT) to 91% at 10 minutes MRT (preferably 4% at 0.4 MRT to 86% at 10 minutes MRT, where the total methyl ester concentration is 0.3 mol/l at 0.4 minute MRT to 2.5 moles/l at 10 minutes MRT (preferably 0.1 mol/l at 0.43 minute MRT to 2.4 moles/l at 10.6 minutes MRT). Preferred Components: The alcohol is a lower aliphatic alcohol (preferably having less than or equal to 10 carbon atoms which is an alkyl, alkenyl or alkynyl alcohol, especially lower alkyl alcohol, particularly methanol, ethanol, propanol, butanol, and/or amyl alcohol). The oil is derived from soy, inedible tallow and grease, corn, edible tallow and lard, cotton, rapeseed, sunflower, canola, peanut, and/or safflower. The catalyst is alcoholic metal oxide, alcoholic metal hydroxide, alcoholic metal carbonate, an alkoxide (preferably sodium or potassium alkoxides), a mineral acid, and/or an enzyme (preferably alcoholic metal hydroxide or enzymatic catalyst).The oil is a triglyceride of formula CH2OOCR3-CH(OOR2)-CH2OOR1. The fatty acid includes at least one site of unsaturation other than a carbon-carbon double bond.R1-R3=10-20C (preferably 12-18C) fatty acids (preferably lauric acid, palmitic acid, stearic acid, oleic acid, linoleic acid or linolenic acid). EXAMPLE - No suitable example given.