Within EPEFE the relationship between exhaust emissions of five 1996 heavy duty engines including advanced technologies and an eleven diesel fuel matrix has been investigated. The fuel matrix was designed to study the effects of decorrelated fuel properties (density, polyaromatics, cetane number, back-end volatility (T95)).The main programme consisted of engine testing on the 88/77 EEC test cycle at standard engine settings. The findings were quantified using regression equations and showed, that fuel effects varied in both magnitude and direction between the four emission components. Individual engines had different emission levels and responded differently to fuel properties, due to engine technology.Additional tests were conducted with selected fuels at adjusted engine settings and timing. The observed density effect on emissions can be compensated for and fully explained by physical interactions with the injection system. A carefully combined optimisation of engine and fuel technologies can lead to a reduction in emissions combined with smaller losses in fuel consumption.