Top Fuel dragsters typically use a fuel blend containing 90% nitromethane. The remaining 10% is generally methanol, creating the familiar nitro fuel associated with NHRA Top Fuel and Funny Car racing.
Nitromethane is valuable in drag racing because each molecule contains oxygen in addition to carbon and hydrogen. That allows an engine to burn a much larger quantity of fuel than it could with gasoline, producing enormous power when combined with a supercharger and a carefully calibrated fuel system.
The 90% figure is a regulated maximum in current NHRA Top Fuel competition, not a claim that the fuel is pure nitromethane. The rule has changed over time: after engine failures in 1999, the limit was reduced, and the 90% maximum returned for the 2008 season.
A common mix-up is treating 99% or 100% as the standard race blend. Pure nitromethane is not the normal NHRA Top Fuel mixture, and the permitted percentage is controlled by technical regulations.