The XPS and AES analyses of virgin surfaces are frequently in disagreement; for example, the carbon and oxygen levels appear much larger by XPS. By rastering an electron beam over the area analysed by XPS it is shown that the XPS analysis changes to become more comparable to that by AES. The initial disagreement is thus due to the interaction of the electron beam used in AES with the surface. SIMS has been used as well as XPS in a preliminary study of the beam interaction with the surface.