The solubilities of palmitic acid in supercritical CO2 and supercritical CO2+water were measured by using a static recirculation method combined with on-line Fourier transform infrared (FTIR) spectroscopy. Experiments were carried out at 15.0 MPa and 313.2 K. The peak of CH2 symmetric stretching band for palmitic acid was used to measure the solubilities of palmitic acid. The solubility of palmitic acid in supercritical CO2 saturated with water was found to be 16% larger than that in supercritical CO2. The interaction between palmitic acid and water was investigated, and the amount of interaction species was determined by using FTIR spectroscopy. The noticeable bands were the C=O stretching bands for palmitic acid. It was also found that the solubility of palmitic acid in supercritical CO2 increased with increasing molarity of water, because of the interaction between water and carboxyl group in palmitic acid. (C) 2003 Elsevier B.V. All rights reserved.