The degradation of middle distillate fuels with increasing time in storage is a continuing problem. Model systems have defined both the scope and the chemical types of molecules that are Implicated in fuel deterioration. To gain insight into a real fuel system, nitrogen-rich extracts have been isolated from a marginally stable shale derived middle distillate fuel and added as a dopant to a stable base fuel in order to induce instability reactions. Alkyl substituted pyridines, tetrahydro-quinolines, quinolines, and indoles were the prevalent classes of compounds present in the extract. The effects of this added extract were examined in terms of sediment formation and peroxide number under accelerated storage stability test conditions. The activity of the extract in inducing fuel instability was correlated with its nitrogen heterocylic composition.