A partially porous mechanical face seal is analyzed. The Reynolds equation is solved analytically and the pressure distribution, leakage, and dynamic coefficients are presented in closed form analytical expressions. It is shown that a partially porous seal has an axial stiffness even in cases of flat parallel faces when solid face seals have no such stiffness at all. A comparison is made between optimally designed partially porous and coned face seals. It is shown that the former give substantial improvement.Presented as a Society of Tribologists and Lubrication Engineers paper at the STLE/ASME Tribology Conference in New Orleans, Louisiana, October 24-27, 1993