Permeability is the property or capacity of a porous rock, sediment, or soil for transmitting a fluid; it is a measure of the relative ease of fluid flow under unequal pressure (¹). The most significant characteristic of mudstones, siltstones and shales are their extremely low permeability. Fine-grained sediments have some of the lowest permeability of any natural occurring mineral, rock or sediment. The porosity of a fine-grained sediment is the major factor that controls the permeability of sediment. The relationship between porosity and permeability of a fine-grained sediment is one of nature’s largest contrasts, one that covers 13 to 15 orders of magnitude. Determining the permeability of fine-grained sediments, that are virtually impermeable, is a difficult accomplishment and can only be achieved accurately by certain geotechnical measurements, such as the consolidation test. Consolidation tests performed on a multitude of fine-grained sediments from the Gulf of Mexico resulted in the determination of the relationships between porosity and permeability of a fine-grained sediment.