The oxides formed on the Sn-Ag coated Large Hadron Collider (LHC) superconducting cables during a 200 degrees C heat treatment in air are described and the oxide composition is compared with the interstrand contact resistance (R-C). The analysis of more than 250 interstrand contact areas shows that the higher the average Cu content with respect to the Sn content in the oxide, the higher is R-C. During the 200 degrees C heat treatment, Sn in the coating is transformed into a Cu3Sn layer, on which an oxide grows that consists essentially of a thin outermost layer of CuO on top Of Cu2O, similar to the oxide structure formed on bare Cu. The underlying Cu3Sn layer acts as an 0 diffusion barrier that prevents 0 diffusion into the Cu bulk during the subsequent cable heat treatment under high pressure. On contact zones where the Cu3Sn layer is not formed during the 200 degrees C heat treatment mainly Sn oxide grows and R-C is comparatively low. (c) 2006 Elsevier B.V. All rights reserved.