How many gallons of gas does a SR-71 Blackbird use?

The answer is both none, and a LOT! None- because the SR 71 does not burn gasoline- it uses a special version of JP-7 jet fuel. The fuel has all sorts of additives to allow it to be used at very high altitudes, lubricate the engine, and reduce the "signature" of the engines. A LOT- which varies. The Blackbird carries around 11,900 gallons of fuel. At takeoff and at lower altitudes, it drinks huge amounts of fuel. However, at VERY high altitudes, and at VERY high speeds, the functions of the engine begin to change from a turbojet to more of a ramjet, and fuel efficiency is much greater. Blackbirds require in-flight refueling from tanker aircraft to replace the fuel they burned climbing to altitude. BTW, aircraft fuel usage is normally measured in pounds, not gallons. JP-7 weighs about 6.75 lbs per gallon.