TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Component: The metal oxide catalyst is alumina, hafnia, titania, and/or zirconia. It may comprise a particulate material.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The method further comprises removing particulates and water from the pyrolysis oil prior to the step of contacting the pyrolysis oil and the alcohol with the metal oxide catalyst. It further comprises removing free fatty acids from diesel-equivalent fuel by binding the free fatty acids to a metal oxide substrate. The contacting step is carried out at 100, preferably 350 degrees C. Pyrolyzing biomass to form the pyrolysis oil includes applying microwave radiation to the biomass under vacuum distillation. Contacting the pyrolysis oil and an alcohol with a metal oxide catalyst results in reducing the acid number from greater than 100 to less than 20, preferably from 112 to less than 13. Preferred Component: The alcohol comprises 1-30C alcohol or ethanol. The biomass comprises corn stover. EXAMPLE - A sample of bio-oil (pyrolysis oil) formed from corn stover using a microwave assisted pyrolysis technique was obtained. The bio-oil was first dissolved in an organic solvent (e.g. ethanol or hexane) to lower the viscosity and ethanol was also used as a reactant. The bio-oil feedstock was then centrifuged at 10000 G for 6 minutes and then filtered through a 5 mu m membrane filter The residence time was held constant at 2 minutes and the reaction temperature was set to 300 or 350 degrees C. Samples of the products produced at both temperatures were then taken and the remaining reaction products were subjected to distillation. The fractions were then analyzed using both H-NMR and gas chromatography-mass spectrometry. The results showed that diesel-equivalent fuel could be produced from bio-oil through a reaction catalyzed by a metal oxide, reaction temperature had a significant effect on the products that are formed in the reaction between bio-oil and organic alcohols, and reaction products produced had a lower acid number and viscosity than bio-oil.