Zirconia promoted with Cs was prepared by cationic exchange of zirconium hydroxide with Cs, then calcined at 550 degrees C, and refluxed in ethanol to remove weakly bonded Cs species. The promotion with Cs stabilized the ZrO2 tetragonal phase and has significantly increased the amount and the strength of the basic sites titrated by microcalorimetry of CO2 adsorption. XPS gave evidence of an electronic enrichment of Zr and O atoms and an enhanced amount of superficial carbonates over ZrOCs. In vegetable oil transesterification, TOFs higher than those of ZrO2, MgAl-HDT, and NaOH were achieved over ZrOCs, demonstrating the potential of this novel solid base. (c) 2009 Elsevier Inc. All rights reserved.