Oxides of aluminum, boron, chromium, calcium, iron, magnesium, manganese, and silicon in carbon steels can be isolated quantitatively by selectively dissolving the iron matrix, phosphides, carbides, and sulfides in a 1:3 mixture of anhydrous bromine-methyl acetate. The insoluble residue can then be filtered, ignited, and analyzed chemically or spectrochemically. Nitrides interefere in this determination, but the only one commonly encountered in plain carbon steels, aluminum nitride, can be eliminated by washing the residue on the filter paper with six per cent sodium carbonate (Na₂CO₃). Tests were run on the National Bureau of Standards 1040 series steel oxygen standards and on a rimmed steel specimen. Test results were in better agreement with certified vacuum fusion oxygen values and were more reproducible than those in which aqueous iodine or iodine-anhydrous methyl alcohol isolation procedures were used.