In any rotating machinery, the geometry of the seal influences the extent of systemleakage. The path taken by the flow in the clearance volume is dependent on the seal and rotor profile. The clearance between a new "seal-rotor" combination is uniform except for small variations during manufacturing and assembly. With time this annular cross section undergoes further physical changes causing non-uniform flow in the annular volume. This azimuthally varying leakage through the seal-rotor annulus creates unbalanced forces on the rotor causing it to whirl. It is essential to identify the reasons for these unwanted forces. Velocity profiling of the clearance volume flow was performed by Morrison et al. (1992) using 3-D LDA measurements on annular and labyrinth seals operating with 50% dynamic eccentricities and a whirl ratio of one. However, this alone does not provide a complete matrix of data for the conditions prevailing in the clearance zone. Additional information of mean and instantaneous wall pressure distributions for 0%, 10%, 25% and 50% rotor dynamic eccentricity for whirl ratios of zero and one, with positive pre-swirl, no pre-swirl and negative pre-swirl conditions were measured by Robic (1999). The data collected showed that the pressure field on the seal walls reversed itself between the whirling and non-whirling conditions. As a continuance of the earlier works, the present effort investigates the effect of whirl ratio variation for a 50% eccentric smooth annular seal at a leakage Reynolds number of 24000. An attempt has been made to collect pressure data for negative whirl ratios also under similar test conditions. A seal test rig capable of handling different eccentricities and whirl ratios simultaneously was designed and constructed for this purpose. Mean and instantaneous wall pressure data were recorded for 50% eccentricity with whirl ratios between ? 1 for a rotor speed of 1800. For a rotor speed of 2700, whirl ratios tested were between ? 0.6 and for 3600 rotor speed, whirl ratios ranging between ? 0.5 were tested. From the collected data a detailed analysis of wall pressures along the seal surface is performed following the technique described by Winslow (1994) and Robic (1999).