Isobaric vapor-liquid-equilibrium (VLE) data at 101.33 kPa for the system formed by benzene, n-heptane and N,N-dimethylformamide (DMF) are reported. Data reduction has been carried out through Wilson, NRTL, and UNIQUAC thermodynamic models for correlating the liquid-phase activity coefficients. Activity coefficients of the components in the mixture indicate positive deviations from Raoult's law. Experimental results show that DMF is a good extractive solvent that reverses the volatility of the binary system benzene + n-heptane.