A simple theoretical model based on the hole theory of the liquid state has been developed in order to find a relationship between the excess molar volume and the excess compressibility of a two-component fluid. The model has been extended to investigate strongly associating fluids dissolved in an apolar solvent. Such a model nicely explains our recent results obtained from a Brillouin scattering study of the nonideal mixture between tert-butyl alcohol and 2-2(') dimethyl butane. Its validity, however, seems to be rather general and it could be usefully applied to rationalize the excess properties of several nonideal binary fluid mixtures.