miles per gallon

i was quite happy with the mileage i got out of the last tank of gas i went through. i'm trying to remember when i last filled up, but i can't. the gas tank holds a little over 12 gallons. i drove 325 miles. that's at least 26 miles per gallon (using 12.5 gallons as the tank size). my serpentine belt is loose an quite squeaky, my check engine light is on (ben rented an automotive diagnostic tool and it says the light means there is something wrong with the emissions control), and i was 3000 miles overdue for an oil change. taking all that into consideration, i'm quite happy with the 26 miles per gallon this last tank. i've gotten over 400 before, but that was all highway miles and my car was a lot younger then. sometime, though, i want to try and reach 500 miles on a tank. i think it can be done. it's not so much how efficient the car is as how you drive. an experiment will most likely take place next year, probably in the spring, to see how many miles i can achieve out of just one tank. cheers . . ..