This work reports experimental and kinetic modeling of the coupled esterification and transesterification reactions ((trans) esterification) of a model acid oil (a mixture of soybean oil and oleic acid) using ethanol at sub and supercritical conditions in a continuous tubular reactor. Process variables, namely temperature (220-350 degrees C), pressure (100-200 bar) and ethanol to acid oil molar ratio (2:1-20:1) as well as the effect of the initial amount of free fatty acids in the raw material were studied. The best condition for the ethylic supercritical (trans) esterification of soybean oil with 20 wt% of oleic acid was 280 degrees C, 100 bar, and ethanol to acid oil molar ratio of 4:1, where 80% of ester yield was reached in 60 min. It was observed that increasing the free fatty acid content increased the reaction rate and reaction yield. The proposed autocatalytic kinetic model presented a good fit in relation to the experimental data.