AbstractThe gas‐chromatographic retention of a series ofn‐alkanes at effectively zero coverage was measured on a poly(ethylene terephthalate) film surface, and the free energy of adsorption per—CH2—segment ofn‐alkane at zero surface coverage, ΔḠ 0A(CH 2), was calculated. This quantity is a direct measure of the London (nonpolar) interactions of the surface. A value of 40 mN/m for γ1/2, the London Component of the polyester surface free energy, may be estimated from the gas‐chromatographic results, in good agreement with results from contact angle measurements. The complete adsorption isotherm and spreading pressure forn‐decane were also measured by finite‐concentration gas chromatography. The method is restricted to polar or crystalline polymers, where then‐alkane does not penetrate the bulk of the materia