INTRODUCTION A thrust bearing surface undergoing an orbital motion is usually encountered in a scroll compressor. In this case the stationary surface is part of the scroll compressor crank case made of gray cast iron ASTM 35 grade and the mating surface is on the orbiting scroll. Orbiting scrolls can be made grey cast iron@ ductile or nodular iron or steel. Steel is expensive and usually offers little strength advantage over ductile iron. Grey iron is usually satisfactory and is lowest in cost. The thrust bearing in a scroll compressor is subjected to an average thrust load of about 1150 lb (5118 N) and speeds of about 3600 rpm (60) Hz in North American market and 3000 rpm (50) Hz in European and Asian continent. Hydrodynamic thrust bearings are usually annular pad bearings in which one of the moving surfaces rotates relative to the other mating surface. Often there will be some type of groove pattern (e.g. radial@ spiral@ or circumferential) on the surface of the rotational thrust bearing to facilitate hydrodynamic pressure generation in the lubricant film and aid in lubricant transport through the groove. It has been known for sometime (Razzaque and Kato@ 1999) that these grooved features@ in the proper size and arrangement@ provide an effective lubrication and load support mechanism. In this experimental investigation for a thrust slide bearing undergoing an orbiting motion it is illustrated that wide and shallow circular pockets arranged around the periphery of the fixed thrust surface will shift the lubrication regime from boundary to full film. Vaidya and Sadeghi (2008) illustrated analytically that in an orbiting thrust bearing usually encountered in scroll compressors@ wide and shallow circular pockets improve thrust bearing lubrication performance as compared to radial circular grooves. Yu and Sadeghi (2001) showed analytically an effective groove method of load support to liquid-lubricated thrust washers. They developed a computational model to solve for the polar-coordinate Reynolds equation using the finite volume approach. In the case of a liquid lubricant@ the geometry of the groove results in cavitation@ a good discussion of which is presented by Broman (2001) as applied to spiralgroove bearings. Thus@ in order to ensure mass continuity@ cavitation was taken into account in Yu and Sadeghi's computational model. They found that grooved thrust washers can support significant loads for rotational motion. Razzaque and Kato (1999) showed the effect of groove inclination on the hydrodynamic behavior of wet clutches. They also demonstrated the effect of inertia in the hydrodynamic performance of wet clutches. Tian et al. (1989) studied boundary lubrication considering ploughing effects; they demonstrated that undulated titanium surfaces would considerably reduce friction coefficient and wear. Andriy et al. (2004) showed that use of dimples expands speed load parameters for hydrodynamic lubrication. The dimensions of the dimples quoted in their studies were 0.002 ?C 0.03 inches (0.05 -0.76 mm) deep and 0.001 ?C 0.02 inches (0.0254 - 0.5) wide. Kulkarni (1990) proposed an approach to design the inner and outer radii of thrust bearing to take into account axial load as well as any twisting moment. Tatsuya et al. (2004) in their theoretical study provided an explanation for the existing lubrication condition at the thrust surface by taking into account wedge formation between the thrust surfaces caused due to the elastic deformation of thrust plate under large loads. This elastic deformation cannot be controlled and hence cannot be used to improve the existing performance. Noriaki et al (2004) in their experimental study showed improvement in the performance of thrust slide bearing by using the pressure difference between the interior and exterior of the thrust bearing. Wang et al. (2002) studied the effect of micro pores formed by laser texturing on a SIC surface. Computational models for smooth surfaces have demonstrated that by properly sizing the circular pockets on the bearing surface@ the shift in the operation of thrust slide bearing (thrust bearing undergoing orbiting motion) from boundary to hydrodynamic full film lubrication regime can be effectively achieved. In this experimental work@ a test rig was designed and developed to enable the direct measurement of the friction@ in a liquid-lubricated orbiting thrust slide bearing under a constant loading condition. This study demonstrates that properly dimensioned macro circular pockets of about 0.002 to 0.003 inch (0.5 to 0.076 mm) deep and 0.3 to 0.36 inch (7.62 to 9.14 mm) wide on thrust washers can support large loads (700 lbs/ 3115 N) at about 3000 rpm with significant reduction in friction coefficient.