* 15 gallons: This was the standard size.
* 19 gallons: Some models, likely those with larger engines or optional equipment, may have had a 19-gallon tank.
To know for sure what size tank *your* specific 2001 GMC Jimmy has, you should:
* Check the owner's manual: This is the most reliable source of information.
* Look inside the fuel door: The sticker on the inside of the fuel door often lists the fuel tank capacity.
Without knowing the specific trim level and options of your vehicle, it's impossible to say definitively which size you have.