Liquid-Liquid Equilibria (LLE) were measured at atmospheric pressure for the binary acetonitrile-water system at temperatures ranging from -1.3 to -18.6 degrees C. Data points were taken using two methods, the cloud point method and the analysis of phase compositions using gas chromatography. Both methods show excellent agreement in their representation of the phase envelope. Temperature dependent NRTL (non-random two liquid) parameters were calculated from the binary data. The parameters calculated were tau(12) = 355.7-31.49T(degrees C) and tau(21) = 967.2-26.59T(degrees C) with the alpha value herd constant at 0.3.