Permeability is the measure of the ease of movement of fluid through the pore space in a rock. Where more than one fluid phase is present (e.g., oil and water), the permeability of one phase is reduced by the presence of the other phase within the pore system. In this instance, the permeability to a particular fluid is called the relative permeability.<ref name=Hawkins /> | Permeability is the measure of the ease of movement of fluid through the pore space in a rock. Where more than one fluid phase is present (e.g., oil and water), the permeability of one phase is reduced by the presence of the other phase within the pore system. In this instance, the permeability to a particular fluid is called the relative permeability.<ref name=Hawkins /> |