Abstract: Herein, a thermodynamic model aimed at describing deoxidation equilibria in liquid steel was developed. The model provides explicit forms of the activity coefficient of solutes in liquid steel, eliminating the need for the minimization of internal Gibbs energy preliminarily when solving deoxidation equilibria. The elimination of internal Gibbs energy minimization is particularly advantageous during the coupling of deoxidation equilibrium calculations with computationally intensive approaches, such as computational fluid dynamics. The model enables efficient calculations through direct embedment of the explicit forms of activity coefficient in the computing code. The proposed thermodynamic model was developed using a quasichemical approach with two key approximations: random mixing of metallic elements (Fe and oxidizing metal) and strong nonrandom pairing of metal and oxygen as nearest neighbors. Through these approximations, the quasichemical approach yielded the activity coefficients of solutes as explicit functions of composition and temperature without requiring the minimization of internal Gibbs energy or the coupling of separate programs. The model was successfully applied in the calculation of deoxidation equilibria of various elements (Al, B, C, Ca, Ce, Cr, La, Mg, Mn, Nb, Si, Ti, V, and Zr). The limitations of the model arising from these assumptions were also discussed.