Experimental results on fluid multiphase equilibria occurring in a series of ternary systems of carbon dioxide + 1-alkanol + o-nitrophenol are presented and discussed. The alkanols considered were 1-octanol, 1-heptanol, 1-hexanol and 1-pentanol. In these mixtures, the critical endpoints of the three-phase equilibria liquid-liquid-vapor were determined experimentally. A comparison of the results obtained in this study was made with previous measurements in a series of ternary mixtures carbon dioxide + 1-alkanol + n-tetradecane with, as the alkanol, 1-octanol, 1-heptanol, 1-hexanol and 1-pentanol. In literature, the binary subsystem carbon dioxide + o-nitrophenol has been reported to have type-V fluid phase behavior according to the classification of Van Konynenburg and Scott, whereas the binary subsystem carbon dioxide + 1-pentanol has type-IV. The other binary subsystems carbon dioxide + 1-alkanol show type-III fluid phase behavior. The transformation of type-V fluid phase behavior into type-IV or type-III suggests that the binary system carbon dioxide + o-nitrophenol actually has type-IV fluid phase behavior instead of type-V. (C) 1998 Elsevier Science B.V. All rights reserved.