Gas mileage and tank capacity

I don't have a manual for my 93 J-30 so I don't know how big the gas tank is. I have only been able to put about 13.5 gallons in this car. My wife drives the J-30 and I drive an I-30 and she only gets about 260 miles out of the car per tank. I reached 290 miles one time. My question is how much gas should this car hold? How much as is in the tank when the low fuel light comes on? How much longer could I drive when the low fuel light does come on? How many miles should I be getting out of a full tank of gas? The reason I'm asking is because of the gas prices and I'm stuck putting $2.35 per gallon in this car for premium. Help!

the tank is 19 gallons, however i think 4 are in the reserve because i can only gas up 15gals and i usually hit about 320miles when i gas up.

I usually just put in about 14 gallons anyway (ends up to be a hare over 30 bux to do it too).

but i don't have a lead foot so i dunno what mileage your supposed to get.



2.35 for premium?!?! u're lucky!!! were at 2.50...

2.79 for plus here

Nan over here $3.00