Experimental work to study the effects of balance ratio, seal face divergency, shaft speed and number of pockets on leakage and tilt stability, for a 9.5 cm pocket-type, hydrostatic rotary end face seal in high-pressure water, is described and discussed. It is shown that leakage and tilt stability, for a given pressure, both depend primarily on balance ratio and parallelity of the sealing gap. It is also shown that seal face separation prevails even if the sealing gap is slightly divergent. For the seal, the data indicate that at least six pockets are required to obtain close to maximum tilt stability.Presented as an American Society of Lubrication Engineers paper at the ASLE/ASME Lubrication Conference in Minneapolis, Minnesota, October 24–26, 1978