A study of the spectral nature of the diffuse attenuation coefficient of light, K(X), for various types of oceanic waters has been performed. These attenuation spectra were computed from downwelling spectral irradiance data Ed(X) obtained by U.S., French, and Japanese in-vestigators working in widely separated oceanic regions and using different measuring techniques and equipment. Attenuation properties were calculated over the spectral region from 365 to 700 nm and for depths from near-surface to in excess of 100 m. Examining the K(X) data, we find that strong, simple, and useful relationships exist between the value of K at some selected reference wavelength, Xo, and the value of K at some other wavelength such that K(X) = M(X) [K(X0)-Kw(X0)] + Kw(X), where Kw is the attenuation coefficient for pure sea water. For oceanic waters (for example, Jerlov types I through III), the relationships are linear. These relationships appear to be useful throughout the entire spectral range examined and are particularly good between 420 and, say, 580 nm. The significance of the existence of such relationships is that they allow the inference of the spectral attenuation coefficient at all wavelengths from the attenuation value at a single wavelength and also provide analytical expressions for modeling the spectral nature of the attenuation in ocean and clear coastal water.