The Ce/Zr ratio of Pd/Ce-ZrO2 catalysts was systematically changed in order to investigate the effect of oxygen vacancy concentration on their decarboxylation activity under solvent-free conditions for potential sustainable petroleum like biodiesel production. Pd/Ce0.5Zr0.5O2 exhibited the highest catalytic activity from all other tested catalysts because it contained the highest oxygen vacancy concentration and Pd dispersion, as shown by the Xray photoelectron spectroscopy, Raman spectroscopy, and CO-chemisorption data. A catalyst deactivation study also showed that both the Pd dispersion and the oxygen vacancy concentration influences the catalytic activity. The catalyst deactivation was found to occur mainly due to Pd sintering, decreases in the BET surface area and Pd dispersion, and partially due to the loss of oxygen vacancies.