Rising fuel prices and global concern over climate change have resulted in the need to deliver vehicles with improved fuel efficiency. The aim is to achieve this without compromising vehicle performance, durability or cost.Passenger car manufacturers worldwide are looking at various ways to optimize fuel economy performance. One option is for a vehicle OEM to re-design engine componentry in an effort to reduce engine friction and thereby reduce tailpipe emissions. There is also an increased focus on the crankcase lubricant as a potential tool to improve engine efficiency. This has led to a close collaborative working model between equipment manufacturers and engine oil marketers to create state of the art fluids capable of delivering higher fuel economy benefits without compromising engine durability.This paper describes a structured approach to the design of an advanced engine oil for a diesel passenger car. The aim of this formulation was to deliver a tangible improvement in fuel efficiency whilst maintaining a high level of engine durability. A carefully designed matrix of crankcase fluids was developed with the intention of investigating the relative effect of key lubricant parameters on fuel efficiency. The fuel economy impact of these formulations was assessed using a vehicle running an industry standard emissions drive cycle on a chassis dynamometer. Selected oils were then taken forward for durability evaluation using an engine test bed. The results of the testing showed that this approach to the design and development of an advanced crankcase lubricant can offer a significant improvement in fuel efficiency without compromising durability when compared to conventional oils.