Studies on cold flow performance have focused on the n-alkane wax precipitating from diesel fuel and their interaction with additives. Little attention has been paid to the solvent system of the fuel. There have been significant changes in the fuel solvent system, due to changes in refining processes and the use of first and second generation biofuels, as well as other components such as GTL.Understanding the extent of the impact of the fuel solvent system change, if and how the change effects wax precipitation, and whether the change influences additive wax interactions, will ultimately enable the optimisation of diesel fuel cold flow performance.This paper first describes a method to characterise diesel fuel solvency. The method is applied to sets of fuels to evaluate the changes in fuel composition over time. A method to replicate the variation in the fuel solvent system is described. The impact of changes in the solvent systems on cold flow properties is considered. Finally, cold flow additive performance is assessed, with the aim of matching the solvency changes to optimise cold flow performance.Using fuel solvency allows improvement in cold flow additive component and formulation design for current diesel fuels. However, it can be used to anticipate changes in fuel quality. For example, by assessing how second generation biofuel components and new crudes from fracking can impact fuel solvency. Therefore, this approach can optimise diesel fuel formulations now and in the future to achieve the best and most economical performance.