Generally, expect:
* Around 18-25 mpg combined (city and highway) for the V6 engines. The specific number will depend on the condition of the vehicle and driving style.
* Potentially slightly lower MPG for the GT model (V6) or those frequently driven in city traffic.
You won't find a single definitive answer without knowing the *exact* engine configuration (it came with several V6 options) of the specific Grand Prix. The EPA fuel economy estimates for that year and model would be the most accurate, but those are hard to find online for individual engine variants now. Checking resources like the EPA's fueleconomy.gov website (if data is available) or a used car listing for a similar vehicle would be your best bet.
