The liquid-liquid-vapor (llg) partial miscibility behavior of the mixture carbon dioxide + n-tetradecane + acetone was experimentally studied by use of a visual cell (stoichiometric) technique. Phase compositions and molar volumes of the two liquid phases in equilibrium are reported as functions of temperature and pressure within the llg region. The addition of the cosolvent acetone extends the three-phase llg region in pressure-temperature space from the binary carbon dioxide + n-tetradecane llg locus downward in pressure, towards the vapor pressure curve of the cosolvent acetone. The three-phase region is bounded from; above by an upper critical end point (1-1 = g) locus, which extends from the binary llg locus to a lower critical end point (1 = 1g) locus, which bounds the region at lower pressures. The degree to which the cosolvent acetone enhances the amount of the solute tetradecane present in the second (carbon dioxide-rich) liquid phase is compared to that of methanol.