Two prominent trends are facing diesel engine builders and their customers, environmental regulations and cost containment. Increasingly stringent exhaust emissions regulations have necessitated major changes in diesel engine design. Combustion temperatures and fuel injection pressures continue to rise. This and other factors, such as lower oil consumption for exhaust particulate reduction, place greater demands on crankcase lubricating oils. Another prominent environmentally related cost factor facing fleet operators is that of waste oil management. The inventory and disposal of used lubricants must now be handled in accordance with regulated guidelines and their associated costs.To compensate, new lubricant categories have been designed in both North America and Europe, such that 1994 and later emission controlled engines will perform as reliably as their earlier counterparts. On the horizon are industry stated objectives to signficantly increase commercial vehicle service intervals (crankcase oil drain interval) for selected commercial vehicle applications. ESI, or Extended Service Interval, is the current industry acronym encompassing the extension of oil changes, filter changes, chassis lubrication and other routine preventive maintenance services. This paper reviews the risks and rewards associated with extending drain intervals and illustrates how laboratory tests may be employed to predict ESI performance. Also, the authors provide linkage with the all important proof of performance--extended (oil) drain field service experience.