Thermogravimetric analysis was used to determine the vapor pressure of the Lippia gracilis S. essential oil. The calibration constant value was obtained using thymol as reference compound, due to the fact that compound represents the majority in the essential oil. To check the calibration, the vapor pressure data for carvacrol have been compared with the results reported in the literature and showed a good agreement. The method was used in the determination of the vapor pressure curve for the essential oil. From vapor curves, the Antoine constants for the essential oil were found to be: A = 10.29230, B = 3116.68 and C = 74.23, respectively. (C) 2013 Elsevier B.V. All rights reserved.