Vapor-liquid equilibria for the binary systems n-butylisocyanate (1-isocynato-butane) + n-butanol, n-nonane + n-butanol, n-nonane + n-butylisocyanate, and N-butylcarbamicacidbutylester (urethane) + n-nonane and for the ternary systems N-butylearbamicacidbutylester + n-butanol + n-nonane and n-butylisocyanate + n-butanol + N-butylearbamicacidbutylester have been studied at (323.15, 338.15, 353.15, and 371.15) K. The measurements have been performed using a specially designed reactor and attenuated total reflection Fourier transform infrared based spectroscopic technique. The vapor pressure and the composition of the liquid phase have been measured simultaneously. The experimental results have been correlated using UNIQUAC and NRTL models, and the binary interaction parameters have been determined. By use of the binary interaction parameters, the VLE of ternary systems is predicted.