A test programme was performed involving two pairs of vehicles - each pair of the same type and model, technically matched, and equipped with emission control systems including lambda sensors and 3-way-catalysts.The aim of the programme was to investigate the influence of gasoline containing 15 ppm Ferrocene (Dicyclopentadienyliron) on the long-term emission performance.Vehicles were operated in a highly comparable way under typical traffic conditions encountered in the FRG. From each pair, one car was fuelled with clear, the other with Ferrocene-containing gasoline.Effects on the exhaust emission performance were explored at intervals of about 10 000 km operation by means of the CVS method using the FTP 75 driving cycle.The results demonstrate that Ferrocene operation resulted in lower pollutant emissions. This was confirmed when one vehicle was switched to Ferrocene operation after 40 000 km of clear operation.Measurements of the fuel economy during test operations showed distinct improvements when vehicles were fuelled with Ferrocene-containing gasolines.Further investigations of particulate emissions from the test cars were conducted by an independent research institute. The results show particulate emission levels to be low, with only minor changes in the particulate iron contents. No gaseous iron compounds were measured within the detection limit.