It is known that the commercial surfactant Dehypon (R) Ls-54 is soluble in supercritical CO2 and that it enables formation of water-in-CO2 microemulsions. In this work we observed phase equilibrium for the Ls-54/CO2 and Ls-54/water/CO2 systems in the liquid CO2 region, from 278.15 to 298.15K. In addition, the Peng-Robinson equation of state (PREOS) was used to model the phase behavior of Ls-54/CO2 binary system as well as to estimate water solubilities in CO2. Ls-54 in CO2 can have solubilities as high as 0.086 M at 278.15K and 15.2 MPa. The stability of the microemulsion decreases with increasing concentration of water. and lower temperatures favor increased solubility of water into the one-phase microemulsion. The PREOS model showed satisfactory agreement with the experimental data for both Ls-54/CO2 and water/CO2 systems. (C) 2010 Elsevier B.V. All rights reserved.