U.S rating is 50 mpg. I usually fill the tank after two hours of high speed driving which amounts to 200KM and the tank will be about half full. Makes a nice interval to stop and stretch old legs. I wouldn´t go beyond 300KM without stopping for fuel as it usually needs to be switched to reserve around that point. Switching over it can have a lag as it takes a few moments to refill the carburetors and they fill slowly with only gravity to move the fuel. Losing power in the fastlane while waiting for reserve to take over is not fun, been there, done that too many times.