The UK government offered a tax incentive to introduce ultra-low sulphur diesel (ULSD) fuels into the market place. This has led rapidly to the use of such a fuel with a consequent reduction in emissions, notably particulates and permits the use of some exhaust after-treatment devices that were formerly precluded.A water-blend fuel technology has been developed to substantially reduce engine out emissions relative to ULSD and is currently under market evaluation. Use of the fuel requires no engine modifications.To further evaluate the emissions performance of the technology, a trial was conducted with the Millbrook testing facility, Bedfordshire, England. The trial also considered the impact of such water-blend fuels on existing/future exhaust emission control technology.On the Millbrook London Transport Bus (MLTB) cycle, the water-blend fuels tested achieved significant reductions in nitrogen oxides (NOx) and particulates over that attained by ULSD. Speciation confirmed that the water-blend fuels tested also gave equivalent or lower levels of unregulated emissions. Further enhancements in total emissions control were achieved through the combination of water-blend fuel with oxidation catalyst and particulate filter traps. No detrimental effect was noted for these fuels with regard to these exhaust emission control technologies.The data from this programme of work illustrate the viability of water-blend fuels in reducing exhaust emissions alone or in combination with exhaust emission control products.