Three cold-rolled steels manufactured under different mill-processing conditions were analyzed by X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and direct oxidation CO2 coulometry (DOCC). XPS and SIMS depth profiling were also used to characterize the steels after successive DOCC oxidative treatments at 450 and 600-degrees-C in order to assess what type of carbon is consumed and what analysis depth is probed at each stage of the DOCC measurement. XPS experiments involving in situ oxidative treatments revealed that, for each steel, all detectable surface carbon is removed at 450-degrees-C. SIMS depth profile analyses determined that Fe2O3 layers formed during the 450 and 600-degrees-C DOCC combustion processes were approximately 200 and 2000 nm thick, respectively, revealing that near surface inorganic carbon is also measured during the DOCC analysis. Nevertheless, it was concluded that the DOCC analysis at 450-degrees-C measures mostly surface organic carbon, since the near surface carbon contribution is minor. The subsequent 600-degrees-C DOCC measurement is comprised entirely of near surface inorganic carbon and is reflective of the process control conditions used to manufacture the steel.