The thermal behaviors of benzoic, sorbic and citric acids, which are three commonly used preservatives, were studied by thermogravimetry. The kinetic mechanisms of evaporation and/or decomposition in air and nitrogen were determined and compared. Benzoic acid completely evaporated via a zero-order kinetic mechanism. Sorbic acid partially evaporated by a zero-order kinetic mechanism, with the production of a transition compound. Citric acid decomposed to a transition compound by a combination of kinetic mechanisms. A majority of the process followed zero-order kinetic principles, with the evaporation of most of the sample. The activation energies of evaporation and the pre-exponential terms were calculated and compared.