If you smell gasoline, it IS NOT the oxygen sensor. The difference from a
bad oxygen sensor will show up on a HC analyzer. The PCM will not just start
dumping gas into the cylinders. I'd suggest that you have someone
knowledgeable look at the vehicle, and figure out where the gas leak is
that's bad enough that it's affecting your mileage. It could be a leaky
injector, or many other things. If you smell gasoline, you are literally
sitting on a disaster waiting to happen.

Man.  That's a pain.  I currently own my first Hyundai ('04 Sonata) and I
like the car - should say my wife likes *her* car.  I know this only applies
to the'06, but it seems there's an increasing number of not-so-routine
things being required by Hyundai to maintain the warranty.  Some things I
can understand, like the timing belt, although a chain would have made that
a moot point.  At some point though, the maintenance being mandated by
Hyundai in order to keep the car under warranty coverage is going to hit the
point that it's more expensive to keep the warranty up than to repair any
other car.

O2 sensors should never be a warranty requirement.  They don't fail at
alarming rates in cars today and Hyundai should be able to put sensors in
that are as reliable as any other manufacturer.  In all of my years of
driving cars that are equipped with O2 sensors, I have only had to replace
one, and that was back in the early years.

Do all Sonata's have three or just the V-6?  I have the 4 cylinder.
Where do you see them having three?  I didn't see the number mentioned.

Matt