This project is concerned with face seal performance under conditions where a phase change may take place. The program is primarily theoretical, but extensive use is made of existing data, industrial experience and ongoing experiments at NASA Lewis, This project will develop more complete and accurate analytical models for steady and transient behavior of face seals and for their stability analyses under a wide variety of practical operating conditions. Current industrial design of high pressure pumps and rotating machinery is moving in a direction where two-phase conditions are definitely occurring in the seal gap as examples, high pressure water pumps and cryogenic liquid pumps. Moreover, in very simple common operating seals the two-phase condition is often present and may dominate the behavior and performance of the seal. A thorough understanding is essential for proper design under such conditions.