The military has unusual requirements for storage of large quantities of fuel for long periods of time as strategic war reserves. Because of the location of these supplies, it is often expensive to remove old fuel and refill the tanks. Thus, recent experience in which Navy distillate fuels have been going off color and showing a tendency to form unacceptable levels of solids in a relatively short period of time has drawn serious attention. This paper will describe the detailed compositional studies of companion diesel fuels that did and did not exhibit problems, with a discussion of the differences observed and the probable mechanisms leading to the problems. Our work suggests that oxidation of neutral components present in fuel to polar intermediates may be a major pathway for sediment formation and darkening of diesel fuels. Within a given compound class, the more aromatic, higher molecular weight members were usually more active in sediment formation.