A method for predicting the location of a dissociation condition on an H-L-w-V line under isochoric operation was presented. To establish the method, the governing equations for the H-L-w-V coexistence under isochoric conditions were derived. Here, a liquid and a vapor phase were expressed by the PR EOS + MHV2 model and a hydrate phase by the van der Waals-Platteeuw model. The molar volume of the vapor phase was calculated from the equation of state, and a simple expression for the molar volume of the hydrate phase was derived. Then, to prove the validity of the proposed method, experimental studies about the dissociation process of the hydrates were performed. The temperature and pressure traces in the hydrate dissociation process, including the location of the dissociation condition, were successfully predicted by the proposed method. In addition, the thermodynamic consistency among the phase models was discussed. It was pointed out that agreement between the calculated and experimental results about the H-L-w-V equilibrium line did not ensure thermodynamic consistency among the phase models. (c) 2005 Elsevier B.V. All rights reserved.