The melting point depression of saturated fatty acids (C-12-C-18) was investigated in liquid or supercritical carbon dioxide. The pressure and temperature melting point ranges were determined for each excipient in liquid or supercritical CO2. Additionally, the effect of pressure on the melting point of fatty acids was also more closely studied in the (7.0 to 50.0) MPa range. Untreated and CO2-treated samples were analyzed by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). A melting point depression in the range (10.8 to 19.5) K was observed for the fatty acids studied in this work. The melting behavior of fatty acids in CO2 was found to be dependent on pressure and carbon chain length. Melting temperature curves for each of the fatty acids in CO2 exhibited a minimum as a function of pressure. Analysis by DSC and XRD indicated that CO2 treatment had no impact on the morphological or crystallographic properties of these excipients under the under the selected experimental conditions.