This experimental work investigates the possibility of reducing the lubricating oil impact on diesel exhaust emissions, particularly concerning the particulate matter, by means of a three-stage experimentation on a Hydra Diesel research engine.The influence of the physical characteristics of the oil was evaluated in the first stage. The results showed that the use of low viscosity oils leads to a better mechanical efficiency and a lower specific fuel consumption than high viscosity oils in the examined viscosity range. Emission tests at a high constant load showed a higher Air Fuel Ratio (AFR) for low viscosity oils compared to high viscosity ones, due to a lesser fuel consumption. As CO, Particulate emissions and smoke are greatly affected by AFR at high load, a decrease of these emissions occurs moving towards low viscosity oils.The influence of the chemical characteristics of the oil was evaluated in the second stage. The tests were carried out by injecting oil components of different chemical nature in the inlet manifold, and recording the emission increase at a high load condition. The results pointed out the effect of some synthetic basestocks that gave a low contribution to particulate emissions. The effect of traditional additives appeared to be less important than the effect of basestocks.A prototype oil, characterized by a 5W-30 SAE grade and by the use of synthetic basestocks selected in the second stage, was formulated in the third stage. The use of such a lubricant gave better emission performances as regards CO, Particulate and smoke, than a mineral 15W-40 oil representative of the European market. The advantage of using the prototype lubricant revealed itself to be comparable with the use of a reformulated low emission fuel. The effects on the examined emissions of both the fuel and the oil emerged as highly significant.Overall the results of the experimentation demonstrate the importance of using a lubricating oil formulated on the basis of reducing emissions criteria.