Permeability that varies with direction of flow through the porous medium. Lateral permeability contrast can be particularly important in fractured formations, where effective permeability in the direction of the fractures may be many times greater than the matrix permeability. If the permeability in one direction is significantly more than in the other, the flow pattern may more closely approximate linear flow than radial flow. This can be detected from well-test data.

Likewise, laminations in most clastic formations cause the permeability normal to the bedding plane to be less than the lateral permeability parallel to bedding. This is called vertical to horizontal permeability anisotropy.