Much of the effort during the final period of this project dealt with interactions between co-dopants added to a stable shale derived diesel fuel. Five classes of nitrogen compounds have been examined in detail. A substituted pyridine and a substituted quinoline behave similarly, exhibiting only minor interactions with t-butylhydroperoxide (TBHP), organic bases and weak organic acids, but forming large amounts of insolubles with a sulfonic acid. Dimethylpyrrole (DMP) interacted strongly with TBHP, weak and strong organic acids to produce increased amounts of sediments but interacted only weakly with organic bases. 3-Methylindole exhibited interaction behavior similar to DMP but the positive interaction was significantly enhanced by venting of sample flasks. Dodecahydrocarbazole showed a distinctive pattern of behavior, a strong positive increase in insolubles with TBHP or tributylamine but a substantial decrease with acids, both carboxylic and sulfonic. Widely used fuel stabilizers were ineffective in reducing sediment formation by 2,5-DMP. An intermediate stream from a shale refining process was moderately stable although it was high in nitrogen content, (2290 ppM w/v). Consecutive treatments with dilute HCl and silica gel significantly improved the stability of this liquid. The extracts contained substantial amounts of pyridines and tetrahydroquinolines with smaller amounts of hydrocarbons and other nitrogen compounds. The most polar of the extracts, that stripped from the silicagel by methanol, was a potent sediment producer, on par with DMP on an equivalent nitrogen basis. Light scattering easily detected formation of larger molecules for stressed shale derived diesel fuel containing DMP. However, formation of copious amounts of insolubles prevented the use of this technique as a useful quantitative tool for evaluating fuel instability. 42 refs., 5 figs., 54 tabs.