The formation of wax crystals in diesel fuels during winter use is a well known phenomenon. The industry has created specifications to insure satisfactory diesel operation under winter conditions by lowering the cloud point with kerosene dilutions or equipment modifications. These specifications create a potential economic penalty to the refiner. An alternate solution to these cold flow problems include the use of chemical additives. This paper will discuss some fundamentals related to the chemical additive approach, namely wax crystal modification.