Reactions that lead to fuel instability can be closely linked to the presence of active oxygen species. An increasing body of evidence links oxidation reactions of hydroperoxides to the instability observed in fuels. The active oxygen compounds present in fuels are alkyl and aromatic hydroperoxides. Cumene hydroperoxide represents a logical choice for an active oxygen compound that could be present in a middle distillate fuel. This paper reports on the reactions of cumene hydroperoxide with octanal in benzene solvent at 140°C for various time periods. The complete slate of products is presented along with a suggested mechanism to explain the observed products and the implications for fuel instability reactions.