The demands placed upon power train lubricants have become increasingly severe with advances in automotive equipment design. Higher operating temperatures, speeds and gear/bearing loads are stressing the capabilities of current mineral oil powertrain lubricants. Gear lubricants based on synthetic fluids provide outstanding service under these conditions and offer a number of performance advantages. This paper reviews the performance of fully synthetic gear lubricants in a variety of laboratory and vehicle tests and comparisons are made with premium mineral oil lubricants. Field testing under severe conditions and extended service periods is also discussed.EXTENSIVE RESEARCH HAS BEEN DEVOTED over the past 40 years to the development of powertrain lubricants of improved performance. Significant advances have been made in lubricant technology to keep pace with advances in powertrain design. While the current generation of gear oils is generally regarded as satisfactory by equipment builders and consumers, lubricants of superior performance, greater versatility and wider applicability remain a desirable goal.