A particular relation between the formation factor (F) and porosity (phi) proposed by the Humble Oil Company. The original formula was expressed as F = 0. 62 / phi^{2. 15}. A nearly equivalent form, with a simpler porosity exponent, is F = 0. 81 / phi². These formulae are considered most suitable for relatively high-porosity, sucrosic, or granular, rocks.

See Winsauer WO, Shearin HM, Masson PH and Williams M: Resistivity of Brine-Saturated Sands in Relation to Pore Geometry, AAPG Bulletin 36 (1952): 253-277.