In this investigation, three possible forms of carbon were identified in mantle-derived material: volatile carbon (methane and carbon dioxide), residual carbon of uncertain location, and carbonate carbon. Volatiles were separated by vacuum crushing, the residuals and total carbon by vacuum fusion, and carbonate carbon by acid evolution. Isotopic analyses of the evolved gases indicate that the residual carbon has a carbon isotope value of approximately -15% to -2%, the volatile carbon gas has a value of less than -21% , and the carbonate about -6.8%, all values being relative to PDB. The different isotopic values displayed by the separate forms of carbon indicate that there are several forms of carbon in the mantle. Carbon as a volatile phase may be of importance in the magmatic and intrusive processes of mantle material upward into the crust.