Abstract: A shaft seal comprises a housing (22) containing a sealing ring (20,720) consisting of a sleeve (24,724) of plastics such as PTFE and an elastomeric ring (30,730) surrounding the sleeve. The dimensions of the sleeve (22,722) are such that fluid can leak between the sleeve and the shaft (10). Fluid pressure is applied to the elastomeric ring (24,724) to apply radial force to the sleeve (22,722) to reduce the leakage of fluid to an acceptable level while maintaining a hydrodynamically stable fluid film between the sleeve and the shaft. The energizing fluid pressure may be supplied from a separate source, or be derived from the system fluid pressure, for example by allowing the fluid to flow through ports (780) in the elastomeric ring (730) to the annular space (748) between the elastomeric ring and the housing. The fluid film between the sealing ring and the shaft reduces wear on the ring and shaft and reduces the heat generated by friction between the ring and the shaft.