What size gas tank in the 01 f150?

The 2001 Ford F-150 came with a few different gas tank sizes, depending on the configuration of the truck (cab size, bed length, engine, etc.). You'll need to check the owner's manual or look at the fuel tank door (often it's printed there) for the exact size for *your* specific truck. They typically ranged from 26 gallons to 36 gallons.