Studies on the hydrogenation of sunflower oil on supported Pd catalysts were performed. The reaction was investigated at 373 K and 413.5 kPa using a semi batch reactor. The adsorption of oleic acid on Pd surface was modeled. The metal catalyst was represented by three low index planes while the oil by cis-4-decene. Besides, two different mechanisms were studied for the cis/trans isomerization and full hydrogenation of the oleic acid: Horiuti-Polanyi and adsorbed monoyne-mediated mechanism. The vis-4-decene model and all the subsequent reaction structures were conformationally studied by molecular mechanics (MM2). The more stable conformations were used as input for extended Huckel like calculations. The theoretical studies show that the selected mechanisms were energetically possible on the Pd planes, however the monoyne-mediated mechanism was more exothermic. (c) 2005 Elsevier B.V. All rights reserved.