The ability to produce chemical state information, i.e. the local bonding environment of an atomic species in question from the topmost few nanometers of the sample makes XPS a unique and valuable tool for understanding the chemistry of the surface. The local bonding environment is affected by the formal oxidation state, the identity of its nearest-neighbor atoms, and its bonding hybridization to the nearest-neighbor or next-nearest-neighbor atoms. For example, while the nominal binding energy of the C electron is 284.6 eV, subtle but reproducible shifts in the actual binding energy, the so-called chemical shift (analogous to NMR spectroscopy), provide the chemical state information.
Chemical-state analysis is widely used for carbon. It reveals the presence or absence of the chemical states of carbon, in approximate order of increasing binding energy, as: carbide (-C), silane (-Si-CH), methylene/methyl/hydrocarbon (-CH-CH-,  CH-CH-, and -CH=CH-), amine (-CH-NH), alcohol (-C-OH), ketone (-C=O), organic ester (-COOR), carbonate (-CO), monofluoro-hydrocarbon (-CFH-CH-), difluoro-hydrocarbon (-CF-CH-), and trifluorocarbon (-CH-CF), to name but a few.
Chemical state analysis of the surface of a silicon wafer reveals chemical shifts due to different formal oxidation states, such as: n-doped silicon and p-doped silicon (metallic silicon), silicon suboxide (SiO), silicon monoxide (SiO), SiO, and silicon dioxide (SiO). An example of this is seen in the figure "High-resolution spectrum of an oxidized silicon wafer in the energy range of the Si 2p signal".