This document is provided to assist in the surface analysis of thin films on materials which are not thought to contain carbon compounds as intended components but for which a C1s peak is observed in the survey spectrum. The films can be those generated on metals and alloys by aerobic or electrochemical oxidation or be those deposited on inert substrates. The procedure described is not suitable for discontinuous deposits of particles on a substrate. With this exception, a simple procedure is provided for identifying the C1s signal from carbon-containing surface contamination. When the C1s peak is identified as arising from an adventitious over-layer the composition derived from the survey spectrum can be corrected for its influence. Recommended procedures are provided in the form of simple Rules structured in the 'If - Then` format with the intention that the information they embody might be utilised by automated procedures in data-systems. The rules provided utilize only information retrieved from the XPS survey scan.