Use of a viscosity increasing component (ii) in provided in a composition (i) of a diesel fuel for the purpose of: improving the vehicle tractive effort (VTE) and/or acceleration performance of a compression ignition engine or a vehicle powered by such an engine, into which engine the composition (i) is introduced, ormitigating decrease in the vehicle tractive effort (VTE) and/or acceleration performance, in the case of a diesel fuel composition (i) to which an additional component (iii) is introduced for the purpose of improving the emissions performance, of a compression ignition engine or a vehicle powered by such an engine, into which engine the composition (i) is introduced.