Previous studies, as introduced by Price and Hawkins [Thermochim. Acta 315 (1998) 19], have established that it is possible to determine the vapor pressures of volatile organic compounds from data collected on a TG unit. This study involves the calculation of the partial vapor pressures of antioxidants by combining the experimental thermogravimetric data with its corresponding reference vapor pressure data obtained with Antoine constants, along with the application of the Langmuir equation for evaporation. The chosen antioxidants for this study are butylated hydroxytoluene and propenyl guaethol. Butylated hydroxytoluene was used as the calibration material from which the vapor pressure curve of propenyl guaethol is proposed. In this study, it was observed that a plot of p versus nu should be sufficient to yield the constant value of k, which is needed for the construction of vapor pressure curves of other samples being studied with the same TG unit. With the aid of a plot of vapor pressure curves with various k-values and a correlation plot, it is established that the k-value as obtained by plotting p versus nu yields a vapor pressure curve that is closest to a given reference vapor pressure curve.