The pressing problems of exhaust emissions legislation on diesel engine manufacturers are well known. A great deal has been written on the engineering modifications necessary so that engines coming onto the market after 1994 meet the relevant emissions standards. Almost certainly engine lubricants will have to be reformulated to meet the increased severity resulting from the modifications. However, there is another aspect to this issue which is seldom discussed, and that is the direct influence of the lubricant on the composition of the exhaust emissions.This paper describes experiments conducted over several years to understand the contribution that the lubricant can make to reducing emissions of NOx and particulate. The first section focuses on how both the physical properties and chemical composition of the lubricant have a role to play in reducing emissions. It then describes the development of a protoype low emission oil. The steps necessary to ensure that the results obtained from emission testing of lubricants are meaningful in light of the repeatability of the various test cycles are also described. Emissions testing has been conducted in both European and North American engines, light and heavy duty emissions test cycles.The final section of the paper describes the development of prototype low emission oils (LEO), and the engine and field testing that is underway to assess their impact on engine durability and cleanliness.