Surface tension data of liquid Al-Cu-Ag ternary alloys have been measured contactlessly using the technique of electromagnetic levitation. A digital CMOS-camera (400 fps) recorded image sequences of the oscillating liquid sample and the surface tension was determined from an analysis of the frequency spectra. Data were obtained at temperatures above the melting point. Samples covered a broad range of compositions. In all cases, the surface tensions could be described as linear functions of temperature with a negative slope. The data were compared to thermodynamic model calculations using the ideal- and subregular solution approximation. It was found that, apart from samples where the composition is close to one of the binary margin phases, the surface tensions of the ternary alloys can be described by the ideal solution model.