Sulfated zirconia (SO4-ZrO2) catalysts, prepared with three different sulfur loading contents (0.75%, 1.8% and 2.5%) at two calcination temperatures (500 degrees C and 700 degrees C), were tested for use in the transesterification of purified palm oil (PPO) and the esterification of palm fatty acid (PFA) in near-critical and super-critical methanol. Techniques including BET, XRD, NH3- and CO2-TPD revealed that the sulfur content and calcination temperature strongly affects the catalyst base-acid site, specific surface area, average pore size, phase structure, and thus the catalytic reactivity. The most suitable sulfur loading content was found to be 1.8% and the optimum calcination temperature 500 degrees C. The results show that the use of SO4-ZrO2 reduces esterification reaction times, the amount of methanol necessary and the required reaction temperature. The reactions at 250 degrees C in the presence of the SO4-ZrO2 catalyst at 0.5 w/w% catalyst to PPO or PFA were found to give the highest FAMEs conversions. Under these conditions, 90% and 75% conversions were achieved within 10 and 1 min from PPO (at 25: 1 MeOH: PPO molar ratio) and PFA (at 6: 1 MeOH: PFA molar ratio), respectively. (C) 2010 Elsevier Ltd. All rights reserved.