During oxidation of SiC small graphitic carbon islands are known to form at the SiO(2)/SiC interface. The parameters influencing the stability of these islands are not known and due to the small size of the carbon islands it is extremely difficult to investigate this problem directly. Therefore we have deposited a graphitic amorphous carbon (a-C) layer onto high duality SiO(2) and investigated the indiffusion of carbon into SiO(2). We have found that if the oxygen contamination of the a-C layer is negligible, no carbon enters the oxide up to the highest temperature we investigated (1190 degreesC). This means that in an oxygen-poor environment the carbon islands can not be dissolved at the usual temperature of SiC oxidation. We find however that if the a-C layer is prepared with oxygen contamination, carbon enters into SiO(2) already at 1140 degreesC. The outdiffusion of carbonaceous species (probably CO) is very fast at this temperature. Therefore, the stability of the carbon islands at the SiO(2)/SiC interface must be controlled by the availability of oxygen.