:This paper discusses the cold flow behavior of diesel fuels with and without the use of cold flow improvers. The flow behavior of diesel fuels at temperatures below their cloud points was first examined. Low temperature optical microscopy technique was used to characterize paraffin waxes that crystallize from fuels at these low temperatures. Crystals were found to grow and form a network that prevented the flow of fuel. The composition of the fuel was found to have a significant effect on its flow behavior.The effect of cold flow improvers on the flow characteristics of fuels was investigated using several analytical techniques. Pour point depressants were found to work as crystal growth inhibitors, where the sizes of the wax crystals were found to decrease from 60 micron to about 10 micron with the addition of the additives. X-Ray diffraction techniques indicated that the orthorhombic crystal structure of waxes in fuels was retained after the addition of the pour point depressants. On the other hand, the operability additives such as the cold filter plugging point improvers were found to work as nucleators for the paraffin waxes in diesel fuels. Crystal sizes decreased from 60 micron to about 1 micron upon adding these additives. The wax crystal structure was found to change from orthorhombic to hexagonal upon the addition of the operability additives. In addition, mixed mode mechanisms of crystal growth inhibition and wax nucleation were investigated.