The objective of this review is to (i) articulate the current level of understanding of the types of “reactive molecules” intimately involved in the long term oxidative storage instability of middle distillates, (ii) review the types of chemical reaction mechanisms most likely involved in the “oxidative phase” of insoluble formation, (iii) review the postulated chemical mechanisms of stabilizer (additive) operation, and (iv) discuss future research areas that must be explored if a greater understanding and control of middle distillate instability is to be realized.