This paper presents the depth distributions of sediment organic carbon, total reduced sulfides, and carbon and oxygen isotopic compositions of carbonates from Sites 767 and 768, ODP Leg 124 in the Celebes and Sulu Sea Basins. Carbonate, organic carbon and sulfide profiles have probably been complicated by changes in sediment organic source input and mode of sedimentation as well as variations in carbonate content during the tectonic development of the basins. £_18O and £_13C of carbonates both generally become lighter with increasing depth. £_13C is more variable than £_18O. The progressive decrease in £_18O with depth may indicate diagenetic formation of carbonates at elevated temperature induced by deep burial and volcanic activity. The highly variable and negative £_13C values in the carbonates indicate an organically-derived CO2 origin of carbon in diagenetic carbonate components.