Catalysts for the removal of sulphur-containing aromatic compounds from diesel fuels were investigated. The target was the "deep" hydrodesulphurisation (HDS) of such fuels down to sulphur levels of 100 parts per million and below, as a means of reducing emissions of sulphur dioxide, and possibly soot, from diesel engines. The project was highly successful. As well as providing important theoretical insights into the behaviour and performance of new catalysts for the target range, there are strong prospects of the results being developed into an industrial-scale HDS process.