An approach to assess host-guest interaction energies in solid inclusion compounds with tunnel host structures is described, based on experimental studies of competitive inclusion of two different types of potential guest molecules X(S)(q)X and X(S)(r)X (q not equal r) within the host tunnel. The proportions (m and 1-m) of the two types of guest molecule included within the host tunnel depend on the proportions (gamma and 1-gamma) of the two types of guest in the external "pool" of potential guest molecules and the relative "affinities" (chi and 1/chi) of the host tunnel for including the two types of guest. Expressions linking chi, m and gamma can be applied to determine chi directly From experimental measurements of m for inclusion compounds prepared with different values of gamma, The value of chi depends on the intermolecular interaction energies per unit length of tunnel for the two types of guest molecule, and chi may be expressed in terms of the host-guest interaction energies for the spacer units S and the end-groups X, and the guest-guest (X . . .X) interaction energy. Preliminary experimental results for urea inclusion compounds containing binary mixtures of alpha,omega -dibromoalkane guest molecules are presented.