21 gallons
I think a 1992 through 2005 Bonnevilles hold about 19 to 20 gallons of fuel. To double check this answer check the owners manual and see if it saids anything on fuel compacity
According to the Haynes manual, 15.2 gallons.
a 1992 Pontiac Bonneville can hold 18 US gallons of gas in its tank.
My 2003 Bonneville SE Holds 18.5 Gallons.
32 us gals 27 imp gal 121 litres