Depends on what specific Oldsmobile you're referring to, Sparky...
18 gallons
24.5 gallons
A 1990 Olds Regency's gas tank will hold 18 gallons of gas.
12.1 gallons
18
After 1996, they hold 20 gallons
most likely 14 to 16 gallons
18 Gallons
16.9 gallons
23 gallons
18.5 gallons
It holds about 15 gallons. Um ehem, It actually hold 18 gallons. The 1999 LSS models only hold 19 gallons.