In 1942 Archie discovered equations which have been used ever since to calculate reserves of oil and gas around the world. Two equations exist, one which is theoretically justified, and one which is not. Unfortunately it is the one which is not justified that often gives the best results. This research examines the extent to which the two approaches give differing results, concluding that the Winsauer et al. form of Archie's equations is better for use with data containing systematic errors.