A sucker-rod pumping system includes diametrically charged rare earth magnets having significant monopolar character mounted on the rod string and, optionally, within a magnet barrel below the pump barrel. The magnets are jacketed to preclude contact with crude petroleum. The magnets subject the petroleum to a significant magnetic flux to substantially preclude precipitation of paraffins and asphaltenes with a minimum of retrofit to existing equipment and without substantially altering the operation of the rod string.