In the prediction of the vapor composition in vapor-liquid equilibrium of the binary system A-B, using boiling points or total pressures as the only equilibrium data, as the concentration of A increases, the nonideality contribution of A changes, not suddenly but gradually, from total, 16/17, 6/7, 4/5, 3/4, 2/3, 1/2... to zero. In addition to the gradual nonideality contribution, by suitable addition of ΔXint to Xint and changing the distribution of the nonideality contribution with the addition, the prediction of vapor composition for systems in which the vapor pressure ratio (PA/PB is much greater than two has become possible. Some forty-two binary systems consisting of Hydrocarbon-Hydrocarbon, Alcohol-Water, Hydrocarbon-Alcohol, and other miscellaneous combinations have been studied and an improved, concise prediction method is illustrated.