One of the most important properties of reservoir rocks, and perhaps the most difficult to predict, is permeability. Laboratory studies have shown that permeability depends on a long list of parameters: porosity, pore size and shape, clay content, stress, pore pressure, fluid type, saturation—a nearly overwhelming complexity. In spite of this, the essential behavior can often be expressed successfully using the remarkably simple Kozeny‐Carman (Kozeny, 1927; Carman, 1937, 1956; Bear, 1972; Scheidegger, 1974) relation κ=Bϕ3S2,where κ is the permeability, ϕ is the porosity, S is the specific surface area (pore surface area per volume of rock), and B is a geometric factor.