A new model developed for predicting the dissociation pressure of gas hydrates proposes that the host-host interaction can he affected by the guest molecules, thus requiring different values of the reference properties, Deltamu(w)(o) and Deltah(w)(o), for each gas hydrate. We presume that the primary impact of the,guest is to distort the lattice, although other factors, such as guest polarity, can have an impact. Experimentally based Deltamu(w)(o) and Deltah(w)(o) values for each gas hydrate show that these values vary from guest to guest, generally increasing with guest size. Using these experimentally determined reference values, the error between calculated and experimental dissociation pressures is reduced. A correlation between Deltamu(w)(o) and the molecular size of the,guest molecule (or the Kihara hard-core diameter 'a') is also developed for estimating values of Deltamu(w)(o) where experimental data are absent (that is, methane in structure II hydrate with no other guests).