Gas hydrates of CO2 in the presence of tetra-n-alkyl ammonium bromide (TBAB) and tetrahydrofuran (THF) show potential applications for storage. Prediction of the phase behavior of these systems is an important precursor for their successful application. In this work, a thermodynamic model is developed to predict phase equilibrium of CO2 hydrates in the presence of TBAB and THF aqueous solutions. In this work, the van der Waals and Platteeuw model is used to model the hydrate phase stability. The fugacity of hydrate former and that of water is calculated from the Peng–Robinson equation of state and the Pitzer–Mayorga–Zavitsas hydration (PMZH) model for TBAB and nonrandom two-liquid (NRTL) models for the THF system. Further, the vapor pressure of water in the empty hydrate as well as Langmuir adsorption constants has been expressed in terms of concentration of the promoter. The model predictions is compared with available experimental data on the phase equilibrium of CO2 hydrates in the presence of TBAB and THF aqueous solution and are found to be in good agreement. Then, the developed model is also applied for the prediction of phase equilibrium conditions of the semiclathrate hydrates of CO2 in the presence of TBAB + NaCl solution. The developed model is found to interpret the promotion effects of both TBAB (with or without NaCl) and THF on phase stability conditions of CO2 hydrate. The overall average absolute deviation in pressure has been perceived to be within 3.6% for TBAB and 7.7% for TBAB + NaCl both with PMZH model and 6.9% for THF systems with NRTL model. © 2017 Curtin University of Technology and John Wiley & Sons, Ltd. StartCopText© 2017 Curtin University of Technology and John Wiley & Sons, Ltd. © 2017 Curtin University of Technology and John Wiley & Sons, Ltd.