Gas Gauge: Terribly Inaccurate

[Newlin]

I've been filling up my tank when it hits 3/4 full recently and the last few days I've been letting it go down to the quarter mark. Anyway it usually takes about 4 gallons to take it from 3/4 to full but the middle half just seemed to drop dramatically. So when I hit a 1/4 tank today I filled her up and it only took a touch over 8 gallons. I've always been under the impression that the tank was 14.1 gallons so is the sensor going bad or is the gauge in the Alero that bad?