A new type of extrathermodynamic relationship is presented: Delta H = T-i[Delta S + R Delta(ln Omega)] + beta, where Omega is the phase volume and beta is a constant. This type of relationship holds for a series of systems in the case where delta Delta(ln Omega) is changeable. The relation between this type of correlation and linear free-energy relationships is shown. An example of the specified correlation for energy parameters of excimers forming in different dipyrenylalkanes is demonstrated.