I Can Get 20 Miles, Even After 120,000 Miles!

I've had my 1998 4 door Pontiac Sunfire for about 4 and a half years now. It's getting old but it has served me very well. As a student I often found myself running low on cash. This resulted in the gas warning light lighting up on more then a few occasions. I've run completely out of gas 2 times. Even with 120,000 miles on the odometer, I can still get about 20 miles before the car completely runs out of gas. It's definitely a bad habit to get into, once you know exactly how many miles you can get after the light comes on you start waiting until the last minute to fill up!