It sounds as though your fuel gauge is wrong or more likely the fuel sending unit located in the fuel Tank is faulty. This Can be caused by contaminated fuel or just a malfunction of the unit
how many gallons are on a 2000 grand prix
23 gallons
Fuel capacity is 14.3 gallons.
about 15 gallons
20 Gallons
20 Gallons
12.7 gallons
17 Gallons.
19 gallons ( U.S. )
( 20 U.S. gallons ) according to my Chilton's book ( for a 1988 Mercury Grand Marquis )
according to the owners manual for my 1987 Grand Wagoneer, it holds 20.3 gallons
according to the website I found, a 1994 Grand Am has a fuel tank capacity of 15.2 gallons