Nanocrystalline diamond films (NCD) are strong candidates for applications in a wide variety of fields. An important concern in all these applications is to understand the properties of variously prepared NCD surfaces. This contribution is focussed on the surface science study of hydrogen and oxygen containing NCD films using X-ray photoelectron spectroscopy (XPS) as well as high resolution electron energy loss spectroscopy (HREELS). Previous studies have demonstrated that hydrogen, oxygen, and gases from the ambient environment as well as water can result in drastic surface changes affecting conductivity, wettability, tribological properties, etc. In this contribution we analyzed differently prepared NCD surfaces as a function of parameters such as the annealing temperature under ultrahigh vacuum conditions (UHV). We are able to identify the thermal stability of a number of species at the interface, which are related to different characteristics of C-H, C-OH, C=O, and C=C bonds. Furthermore, a formation of graphitic-like species appears at higher annealing temperatures. An atomic hydrogen treatment was also applied to the NCD surface to obtain further information about the surface composition.