Perfluoropolyether (PFPE) films for lubrication of thin film magnetic recording media are made progressively thinner and their physical properties are increasingly dominated by molecular interactions with the carbon overcoat. Surface potential measurement is one of a few techniques to study the interaction of ultrathin films with surfaces. A scanning Kelvin probe apparatus with spatial resolution of 100 microns and potential sensitivity of 0.5 mV was employed to study the surface potentials of linear and branched PFPE films with methyl, hydroxyl, phenyl ester, and carboxylic acid end groups on amorphous hydrogenated carbon surfaces. The surface potential is dominated by polar groups rather than the PFPE monomers. Application of the scanning surface potential technique to measure the migration of PFPE films is also shown. ©1997 American Institute of Physics.