Diesel engines are prime movers on a world wide scale for heavy duty trucks. Their market share in passenger cars, however, varies considerably between countries; depending on fuel prices, local fuel/car taxation and acceptability to private motorists. Pressures to reduce fuel consumption (CO2 emissions) and operational costs have increased the market share of diesel engines in new car sales to over 40% in some countries. At the same time diesel engine technology for trucks, buses and passenger cars has improved considerably with significantly higher performance, lower emissions and excellent customer acceptance.To reach all these goals, fuels, lubricants and coolants must meet high quality standards. In this respects fuel additives can contribute considerably to such performance aspects, and improve fuel quality in a cost effective manner.For example, ignition improvers lead to better combustion which results in lower exhaust emissions, better fuel economy and improved cold start performance.Similarly detergent additives keep vital engine components (particularly the fuel injectors) clean so that performance, fuel economy and emissions levels do not deteriorate over the life time of the engine. Both additives also lead to lower engine noise emissions.As another example, the conflicting demands for optimum combustion (which means high cetane quality paraffins) and low temperature operability, i.e. avoidance of paraffin waxing can be resolved by tailored cold flow additives. Additives can be used to enhance the lubricity of low sulphur fuels to protect rotary injection pumps and unit injectors. Finally, the handling aspects of diesel fuels can be improved for the customer through the use of anti foam additives to reduce filling times and fuel spillage.Diesel fuel additives therefore have the potential to improve the quality of diesel fuels with regard to emissions, noise, engine performance and customer perception whilst offering flexibility in the optimisation of refinery production costs.