Vapor-liquid equilibria of different lactones, gamma-butyrolactone, epsilon-caprolactone, gamma-caprolactone, gamma-decalactone, and a delta-lactone with supercritical CO2 have been measured applying the synthetic method using a high pressure view cell with variable volume in a temperature range from 313 to 363 K and in a pressure range from 9 to 27 MPa. The experimental data have been reasonably correlated using the Peng-Robinson equation of state (PR-EOS) combined with the Margules mixing rule. The binary critical points determined from the different isotherms show a type-II phase behavior for most of the systems, but indicate a type III or even a IV behavior for the delta-lactone. (C) 2002 Elsevier Science B.V. All rights reserved.