Fuel is the single largest operating expense for a diesel truck fleet. This paper presents data on the many factors which affect consumption, and on the ways in which fuels and additives can contribute to minimizing it. Fuel density is the key fuel parameter affecting consumption, since higher density fuels deliver more energy per litre than those of lower density.Diesel cold flow improver additives can play an important role in the economic production of diesel fuel. In addition, they allow the production of higher density fuels while maintaining good low temperature performance. Dynamometer test data are presented to show the effects of ambient temperature, vehicle speed and fuel density on consumption. The performance of flow improver additives in improving low temperature operability while maximizing density is demonstrated.Finally, field test data are presented which show that the improvements due to higher fuel density can be greater than predicted from steady speed fuel consumption tests. These results are confirmed in a dynamometer test, carried out under dynamic operating conditions.