Abstract: An improved sealing system for a rotary rock bit retains lubricant inside the bearing area of the bit and acts as a barrier to the pulverized cuttings and other materials in the borehole to prevent the materials from entering the bearing area through the cone mouth opening of the rolling cone cutter. An annular seal member located in the cone mouth opening has a hollow core filled with a fluid. The fluid will flow thru the hollow core when pressure is applied. During drilling with a rotary rock bit the lower or loaded side of the bearing has less clearance than the upper or unloaded side. The pressure on the loaded side of the bearing will force the fluid to the unloaded side of the seal member and cause that side of the seal member to expand and fill the clearance to maintain a seal.