The pendant-drop method combined with axisymmetric drop-shape analysis was used to determine liquid-vapor and liquid-liquid interfacial tension of mixtures consisting of heptane (1), toluene (2), and N,N-dimethylformamide (3). The method of pendant drop with an efficient temperature control of the measuring cell allows precision measurements of surface tension and interfacial tension. Surface tensions and liquid densities of more then 20 ternary mixtures in the homogeneous region were determined at a normal pressure of 1 bar and over a temperature range from 287 K to 317 K. Inside the miscibility gap of this system, liquid densities in both liquid phases using buoyancy experiments dependent on temperature were obtained. Furthermore, the pendant-drop technique allows measurements of the interfacial tension between the two liquid phases even close to the critical solution point for the ternary mixture. The resulting interfacial tension and the density difference vs temperature up to the critical solution point could be well described using a Wegner-type expression.