The oxidation behaviour of various boron-carbide samples have been studied by photoelectron spectroscopy. The exposure of sputter-cleaned surfaces to molecular oxygen at room temperature did not cause a measurable surface oxidation. An increased reactivity has been found by irradiating boron carbide with energetic oxygen ions. The highest reactivity against oxidation was obtained during the growth of a boron-carbide surface phase which revealed a marked oxygen gettering effect.