2004 Volvo XC90 Gasoline order

If it's a slow leak in the bottom of the gas tank then you might not see any evidence since gas evaptorates pretty fast. Or it could be a hole in the top of the gas tank that you can't see but can smell. Also, it could be a leak somewhere in the engine that only occures while you're driving, and then when you park it in the garage all the leaked gas on your engine starts evaporating and creating the smell in the garage. Also, I doubt this, but maybe your car isn't leaking at all, and the smell in the garage is from some other gas source such as an open container of lawnmower gas or something. I doubt this too, but maybe the gas cap on your fuel tank is messed up and not sealing properly

Most likely your fuel pump is leaking. It is located on top of the tank. You would need to remove the second row seats and maybe third row to access the pump. Have local mechanic or dealership fix this problem ASAP.