Alkanethiol self assembled monolayers of varying chain lengths have been studied by X-ray photoelectron spectroscopy. Inelastic background of the S2p peak monotonically increases with the chain length. The binding energies and peak shapes are the same for all the samples studied indicating the chemical similarity of the monolayers. However, increased packing density is seen with hexane and octanethiol SAMs suggesting greater surface order. It is proposed that in higher and lower thiols, random orientation of the chains decreases packing density. Inelastic background of the S2p peak is directly proportional to the ellipsometric thickness of the monolayers. © 1998 Elsevier Science Ltd. All rights reserved.