Liquid-Liquid equilibria for water + benzonitrile f formamide, water + benzonitrile f N-methylformamide, and water + benzonitrile + N,N-dimethylformamide were studied in the temperature range 25 degrees C-45 degrees C with analysis by gas chromatography. Phase diagrams, including experimentally determined tie Lines and plait points for the systems including substituted formamides, are reported at each temperature. Distribution curves and enthalpy of transfer values of the amide from benzonitrile to water are given. Solubility of benzonitrile in formamide and of formamide in benzonitrile is estimated as a function of temperature.