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 megasupramolecules to dissociate and reassemble. These new polymers may find application in fire-safer fuels and as rheology modifiers in diverse organic liquids.