A stuffing box for a wellhead comprises a stationary housing defining a passage for receiving a well tubular, and a tubular shaft mounted on the stationary housing for rotation within the passage and defining an inner axial bore. The inner axial bore is adapted to form a static seal around the well tubular in use, and a dynamic pressure seal is mounted within an annular cavity defined by respective cylindrical surfaces of the stationary housing and the tubular shaft. One or both of the respective cylindrical surfaces are tapered to decrease the radial cross sectional area of a seal travel portion of the annular cavity in an axial direction from a well end of the stationary housing to an opposite second end of the stationary housing.