Recent contact angle studies provide an experimental foundation for theoretical developments of molecular interactions. These newly obtained contact angles are interpreted in terms of combining rules for solid-liquid intermolecular potential. Results suggest that existing combining rules do not describe adequately the experimental adhesion patterns-the calculated and experimental patterns differ considerably. It is shown that the combining rule originally proposed by Hudson and McCoubrey can be improved to advance our understanding for solid-liquid interactions from like pairs. Macroscopic contact angle measurements are used to infer relationships of unlike solid-liquid interactions at a molecular level. The resulting combining rule gives a good fit to experimental adhesion and contact angle patterns for the range studied. The thermodynamic property solid surface tension can also be obtained from this relation.