Amorphous zirconia catalysts, titanium-, aluminum-, and potassium-doped zirconias, were prepared and evaluated in the transesterification of soybean oil with methanol at 250 degrees C, and the esterification of n-octanoic acid with methanol at 175-200 degrees C. Titanium- and aluminum-doped zirconias are promising solid catalysts for the production of biodiesel fuels from soybean oil because of their high performance, with over 95% conversion in both of the esterifications. (c) 2006 Published by Elsevier Ltd.