If it is indeed fuel that you are smelling, coming from the vents, I suggest that you figure out what is going on IMMEDIATELY!!!!!
Id check under the hood, near the back of the engine, where the fuel lines are located, for any leaks.
There are not any fuel lines that are inside of the car or in the A/C or ventilation system. The engine coolant DOES run through the HVAC box, though, and if the heater core begins to leak there can be a very strong coolant odor coming from the vents.
So that's another possibility.
If you think that you smell gasoline, get the car checked out before you drive it anymore.