It could be just water from condensation coming from the tailpipe and maybe the gas smell is coming from somewhere else on the vehicle. Otherwise you have unburned fuel coming out the tailpipe which is an engine problem.
It is more than like just condensation dripping that has condensed in the exhaust pipe. However if it is actually fuel then do not drive it and contact a mechanic. It could be very dangerous.
It is probably either a pinhole in your gas tank or a gasline that has a pinhole in it. Get under your car and look to see if you can find a trail since the gas tank is right about the tailpipe.
