High oleic sunflower oil was processed at high temperature and high H2 pressure in a batch reactor using different catalysts and reaction conditions for its derivatization to biogasoil (mixture of parafines and isoparafines suitable as biofuel for diesel engines). The product from processing oil at 350 °C and 100 bar of H2 for 2h using NiMo/Al2O3 or CoMo/Al2O3 as catalyst did not contained hydrocarbons, although a high concentration of catalyst was used (5 %). Instead, free fatty acids (FFA) were the major component of this product (83 %), showing that hydrolysis highly predominated over the desired hydrodeoxygenation reaction (HDO). However, under the same conditions but using only 1.0 % of PtO2 as catalyst the formation of hydrocarbons was verified: C17:0 (4.0 %) + C18:0 (12.9 %) and, accordingly, the percentage of FFA diminished to 55 %. When this product (containing the used catalyst) was reprocessed for 3 additional hours but performing regular purges of the gas from reactor head space (every 5-10 minutes) followed by gas replacement with fresh H2, hydrocarbons concentration raised to 51,3% and FFA concentration diminished to 24 %. Additionally, after a third processing under same conditions a product containing 87.3 % hydrocarbons and only 2.9 % FFA was achieved. Hydrocarbons fraction comprised C18:0 (69.2 %), C17:0 (24.6 %) and other shorter chain length hydrocarbons at concentrations under 1%. Product composition suggest that, although HDO was the main process, decarbonylation, decarboxylation and hydrocracking must also have occurred. Purging the system produced a drastic favorable effect on process performance indicating that the removal of the main gas products generated by the reaction (H2O, CO2, CO and C3H8) kept them at low partial pressures, increasing H2 partial pressure and shifting HDO reaction to almost completion.