1996 Chrysler Concorde Fuel economy or leak

Engine Performance problem
1996 Chrysler Concorde Four Wheel Drive Automatic 75000 miles

My 17-year-old put gas in his car at the end of last week and when was leaving the gas station he noticed a pooling of gas on the ground.

When he came home, he told me about it. I told him to put cardboard under the gas tank and we would check in a few minutes. 20-min later nothing. I had him bump the car up and down while I looked under and I seen gas flowing out from the top. But not where at.

The research I have done says it might be a overfil guard. I don't know anything about those.

5 days later his gas tank is already on 1/8 of a tank! He says he has a thing inthe car that tells him how much gas milage he is getting and he says it is reading 17 miles per gallon! Is this right for this car?

It is the manufactured engine. If that helps.
uuuuggggg trouble.