a pressure balanced mechanical seal , especially adaptable for use in a swivel in an oil well drilling arrangement comprising a pair of relatively rotatable seal rings constructed of silicon carbide or tungsten carbide each received in a cavity defined by a cylindrical and a radial wall in the respective housing for the ring with the inner cylindrical surface of each exposed to high pressure , high temperature drilling mud and with means to communicate drilling mud to the outer cylindrical surfaces thereof , and means for balancing the axial forces on the rings and to insure sufficient axial forces for perfecting the seal . tensional and compressive forces on the rings are minimized insuring reasonable life to the seal , far in excess of that in the conventional packings now used in the oil drilling system .