The aim of the present work was to understand and develop a model to describe the changes resin acids undergo during pine oleoresin processing. Experimental data for the thermal isomerization of levopimaric acid, in the temperature range 155-200 degrees C, were used to develop a kinetic model. Model validation was based on the experimental results from the batch distillation of pine oleoresins. Both the experimental activation energy and pre-exponential factors seem to change during the course of distillation, due presumably to solvent (turpentine) removal.