Volumetric behavior was measured of carbon dioxide + butan-1-ol mixtures at 313.15 K using a vibrating tube density meter. The saturated pressures were also measured of carbon dioxide + butan-1-ol mixtures at 313.15 K by the conventional synthetic method. The equilibrium vapor compositions were newly evaluated by combining the molar volume equation, the experimental values of the equilibrium vapor density, vapor density of pure carbon dioxide, and pressure.