In this work, a prediction model was studied and carried out to predict phase equilibrium conditions for semiclathrate hydrates formed from the ternary system of liquid water, tetra-n-butyl ammonium bromide, and CO2, CH4, or N-2. Based on the Soave-Redlich-Kwong equation of state along with the Chen-Guo model, the predictions of phase equilibria of semiclathrates of CO2, CH4, and N-2 + pure water/tetra-n-butyl ammonium bromide aqueous solution has been made. A new correlation for activity relating to the system temperature and tetra-n-butyl ammonium bromide concentration has been proposed. The prediction results were analyzed and showed good agreement with the experimental data.