Rubber compounds are complex mixtures of ingredients, including many mobile and volatile species. Exposure to the ultrahigh vacuum environment common to surface analytical instruments can therefore cause significant changes in a rubber surface and produce misleading and even erroneous results. In this work it has been shown that stable, representative x-ray photoelectron spectra could be obtained if the specimen was precooled below a compound-dependent maximum temperature before exposure to the vacuum environment. Maximum temperatures were found to be -50 and -70 degrees C for two typical tire rubber compounds, a wire adhesion formulation and passenger tire tread, respectively. Effects of specimen preparation were further investigated. High resolution x-ray photoelectron spectra of specimens precooled to -85 degrees C and analyzed at -140 degrees C indicated a correlation between the sulfur peak positions and the length of sulfur cross-links in the rubber. Specifically, a linear relationship was found between sulfur 2p binding energy and the percentage of monosulfidic and polysulfide cross-links as determined by standard bulk solvent swelling analysis for three different rubber compounds based on two different polymers. (c) 2007 American Vacuum Society.