This document describes a method for the determination of oxygen content and carbon-to-oxygen ratio in graphene powders using X-Rays photoelectron spectroscopy (XPS). The scope of application includes the determination of graphene powders, graphene slurries, and Miscellaneous carbon-based nanomaterials. The normative reference documents cover the general principles of X-Rays photoelectron spectroscopy analysis methods, the calibration of X-Rays photoelectron spectrometer energy scales, the reporting of X-Rays photoelectron spectroscopy charge control and charge correction methods for surface chemical analysis, and the handling of samples before analysis. The terms and definitions section defines related concepts such as graphene, graphene powder, and graphene oxidation.