The present study has been undertaken to evaluate the basicity concept of oxygen content estimation subject to submerged arc welded metal. The investigated fluxes cover a wide range of basicity indices from 0.31 to 19.00 at full coverage with acidic, neutral, and basic fluxes. The oxygen content of the submerged arc welded metal (flux oxygen potential) is predicted by employing traditional flux basicity index models and the CALPHAD technique (gas–slag–metal equilibrium model). It is revealed that the gas–slag–metal equilibrium model in this study is capable of remedying the shortcomings of the basicity index models with respect to predicting the oxygen potentials of the fluxes with CaF₂, CaO, SiO₂, MnO, and FeO as major components. This study may provide a vital way to address technical difficulties in flux design. Based on the measured and thermodynamic data, thermodynamic parameters pertinent to flux oxygen potential have been systematically assessed.