The dense phases of the CO2-CCl4 (I) and CO2-CS2 (II) mixtures have been studied by Raman spectroscopy. Mixture I is found almost ideal and II strongly non-ideal. At high CS2 concentration in II, the local structure of CS2 is preserved suggesting a nano-segregation of the liquid phase without demixing whereas in CO2 concentrated mixtures a diversity of species are present. Thermodynamical considerations together with spectroscopic results show that a subtle interplay between attractive and repulsive interactions leads to this non-ideal behaviour. The connection of these results with the liquid-liquid demixing reported for CO2-CS2 at lower temperature is discussed. (C) 2013 Elsevier B. V. All rights reserved.