Liquid fuels (petroleum, diesel, kerosene, etc.) are the world's dominant power source (34% of global energy consumption, 32.5 Billion barrels/year). Transportation relies almost entirely on liquid fuels, presenting the constant risk of explosive combustion in the event of impact. A sobering example is the role of the initial fuel explosion in the collapse of the world trade center towers on September 11, 2001. To mitigate post-impact fuel explosions, we have synthesized and characterized long end-associative polymers that form “mega-supramolecules,” which control impact-induced misting. Statistical mechanics guided design of the length of the polymers, strength of end-to-end association and concentration. Engineering tests confirm that they burn cleanly in unmodified diesel engines with no adverse effect on power output, fuel efficiency or emissions. In fact, they provide a 12% (p=0.002) reduction in the formation of toxic diesel soot. The drop size in post-impact mist shifts to larger sizes when fuel is treated with these polymers, preventing flame propagation (hence, no fireball). Mega-supramolecules also provide drag reduction like ultra-long polymers—without the problem of “shear degradation” (e.g., during passage through pumps, pipelines and filters), thanks to reversible associations that allow the mega-supramolecules to dissociate and reassemble. These new polymers may find application in fire-safer fuels and as rheology modifiers in diverse organic liquids.