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
a 1992 Pontiac Bonneville can hold 18 US gallons of gas in its tank.
My 2003 Bonneville SE Holds 18.5 Gallons.
21 gallons
16 gallons
12.7 gallons
20.9 US Gallons.
18 gallons found at http://www.new-cars.com/2003/pontiac/pontiac-aztek-specs.html
14 gallons
16
13.25 dry.
About 12 gallons in my 2003 ==According to Haynes,== 15.2 gallons. FriPilot
16.5 gallons.