The effects of low dissolved oxygen concentrations on fuel thermal stability are far from being understood; however, such an understanding is essential for aircraft fuel system design. Experiments were conducted using a flowing system in which the dissolved oxygen level at the entrance of the apparatus is varied. One of the most intriguing results of these experiments is the increase in deposits in heated sections for decreased oxygen consumption. This observation is seemingly contrary to nearly all previous observations concerning the relation between deposit formation and oxygen consumption. For a given system, there appears to be a least favorable dissolved oxygen concentration which produces the maximum amount of deposits. In addition, the deposition mechanisms in heated locations were quite different from those in cooled regions.