Isobaric vapor-liquid equilibrium data of the ternary system benzene + n-heptane + N-methylpyrrolidone (NMP) have been measured with a Rock and Sieg recirculation still at 101.33 kPa. The experimental data reported were thermodynamically consistent when tested by the McDermott-Ellis method. Data were correlated with the Wilson and NRTL, equations for the liquid-phase activity coefficients. Activity coefficients of the components in the mixture indicate positive deviations from Raoult's law. Experimental results show that NMP is a good extractive solvent that reverses the volatility of the binary system benzene + n-heptane.