Absolute surface areas of a set of seventy-five representative deep-sea core samples have been measured by the gas-adsorption method. The values range from $2.5 m^{2}/gm$ for fine red silt to $48.0 m^{2}/gm$ for some continental clay but are characteristic of a specific sediment type. In the most common sediment, a pink to gray foraminiferal clay, the surface areas vary from about 7 to about $30 m^{2}/gm$, depending largely on the concentration of the Foraminifera shells. Pertinent aspects of the theory and the technique of this method of surface-area measurement are presented.