* Gasoline: The most common fuel option for the 2004 A8 was gasoline.
* Diesel: Some models came equipped with a powerful diesel engine.
* Biodiesel: The 2004 A8's diesel engines could potentially run on biodiesel blends, though this was not officially supported by Audi.
To determine the specific fuel type used by your 2004 Audi A8, you can consult the owner's manual or the vehicle identification number (VIN).