1ABSTRACTSince 1997 the ELF group has been working on a new fuel designed in priority for use with urban services (buses, lorries). Basically, it is a diesel/water emulsion stabilised by a series of new additives.A lot of testing programmes on engine and vehicles test benches was carried out. They have clearly shown that with this new fuel there is a reduction of nitrogen oxide emissions by up to 30% and black smoke by up to 80%, without any technological modifications being necessary as against EN 590 diesel fuel marketed normally. The water content is, however, the cause of a certain loss in engine performances. Nevertheless, hydrocarbon consumption is reduced by up to 4%.The use of an oxidation catalyst is compatible with a water-diesel emulsified fuel and results in larger emission benefits. Furthermore, a 50 ppm sulphur emulsion with a continuously regenerating particle filter give a particle reduction of 90%. Thus the NOx effects obtained by the fuel can be combined with an after-treatment.Beginning January 2000 more than 1000 vehicles run daily on Aquazole™, covering 3 million km per month.