Raman spectra of ternary mixtures of unknown composition are processed to extract the content of the compounds in the mixture. The evaluation method of the ternary mixtures is based on a previous calibration of binary mixtures. The applicability of the method is demonstrated by measuring the vapour liquid equilibria of the ternary system carbon dioxide, ethyl acetate and water at 8.5 MPa and 310K and providing them in a triangle diagram. The advantages of the used flexible Raman sensor in comparison to conventional techniques for the determination of phase equilibria are discussed. (C) 2013 Elsevier B.V. All rights reserved.