A new thermodynamic model is presented to determine gas hydrate equilibrium in sediments. Using variable contact angles between water and gas in pores, we obtain more accurate prediction of the equilibrium condition of gas hydrates in the sediment than previous studies that used a constant angle of zero. An empirical correlation between variable contact angles and gas solubility is determined in terms of experimental data and is used in the thermodynamic calculations. The new variable contact angle model can reduce the prediction error for equilibrium pressure by more than 50% compared to the Clark-Bishnoi model for temperatures > 274 K. (c) 2005 American Institute of Chemical Engineers.