Liquid-liquid equilibria of binary mixtures of water and dinitrile solvents malononitrile, succinonitrile, and glutraronitrile have been studied in temperature range of 15 to 70 degreesC. The phase diagrams show that the critical mole fraction and consolate temperature (degreesC) (x(c), T-c) are (0.25, 58) for malononitrile and (0.19, 56) and (0.12, 68) for succinonitrile and glutraronitrile, respectively. The nonrandom two-liquid (NRTL) equation has been used to correlate of the activity coefficients of the components in binary mixtures. The parameters needed for the calculation are the energy parameters (g(12) - g(22)) and (g(21) - g(11)) and the nonrandom parameter alpha, which are determined by solving the NRTL equation with the aid of a nonlinear least-squares curve-fitting program. From the parameters of this equation, the excess Gibbs energies, G(E), were calculated. Good agreement between the experimental data of phase diagrams and model results was achieved.