In this work, the Butler equation is assessed for evaluating the liquid/gas surface tension for three compositions in the ternary $U −Zr−O$ system over a wide temperature range 2600−3100 K. In this approach, the liquid phase Gibbs energy is obtained from two CALPHAD-type databases, NUCLEA and TAF-ID. Two formulations of the Butler equation makes use of an ideal phase mixing hypothesis (φ being the weighting factor) with and without surface tension laws for pure components. A third formulation corresponds to the classical form of the Butler equation found in the literature where the interfacial Gibbs excess energy is assumed to be proportional to to the liquid one (the multiplicative factor $k_Γ$ being related to the ratio of broken bounds). Computed surface tensions are compared to experimental values obtained by C. Denier in her Ph.D. thesis in the VITI facility at CEA Cadarache. Three different compositions corresponding to different Zirconium oxydation degree, C0, C30 and C50 are considered. It is shown through a limited parametric analysis that the choice of the CALPHAD database affects both the slope w.r.t temperature and the level of the interfacial energy while parameters $\phi$ and $k_Γ$ mainly affects the level and only slightly the slope. Considering pure component surface tension data has a significant impact on both and, considering the C0 composition measurements, it is shown that parameters $\phi$ and $k_Γ$ can be successfully calibrated for reproducing these data. However, the steep variation of the interfacial energy w.r.t temperature exhibited by experimental results for the C30 composition is, in any case, not correctly captured. This shows the need for further improvement of the liquid thermodynamic modelling and a path forward is proposed.