How many gallons of gas will a 1997 Toyota Avalon gas tank hold?

18.5 gallons (to be exact... 70 liters)

It's the same tank as my 1998 Avalon. You should get about 16.0 gallons until the yellow gas indicator light comes on. I have found the light comes on earlier or later depending on how your car is angled (ie: going up a hill or coming down). I Hope that helps. :D