The resistance of ceramic matrix composites to combust at high oxygen pressures is expected to provide information in developing oxygen-rich propulsion systems. In contrast to metals, silicon based ceramics, SiC, Si3N4 and SiC-composites, have prevalently covalent bonding characteristics and their promoted combustion characteristics were different. These materials dissociate at very high temperatures rather than going through discrete solid-liquid phase transformation (melting). The silicon based ceramics and composites burn heterogeneously at very high oxygen pressures and the critical threshold pressure at which no test specimen sustains combustion correlated with composition, the nature of the bonding and the solubility of oxygen. (C) 2004 Kluwer Academic Publishers.