In this study, a novel approach to converting fatty acids into n-alkanes was investigated. Fuel range hydrocarbons were obtained in a continuous flow process from oleic acid using near- and supercritical water as the reaction medium, granulated activated carbon as a catalyst, and 1% v/v formic acid as an in situ source of hydrogen. Experiments were conducted in a packed tubular reactor with the weight hourly space velocity of 4 h(-1) at temperatures from 350 to 400 degrees C and pressure 3500 psi (24.1 MPa). The oil to water to formic acid ratio was 1:5:0.05 by volume. The main reaction pathways were hydrogenation of oleic acid and decarboxylation/decarbonylation of the resulting stearic acid to form heptadecane. The yield of heptadecane of above 70% with a selectivity 80% was observed between 370 and 380 degrees C. The results of the study show that efficient hydrothermal deoxygenation of fatty acids can be achieved with activated carbon as a catalyst and formic acid as an in situ source of hydrogen within minutes. Kinetics study showed that the rates of oleic acid conversion displayed Arrhenius behavior with an activation energy of 120 kJ/mol.