Ray wrote:
I spilled a fairly large amount of a gasoline additive on the floor
of my
car, and now I can hardly get in it.

The additive smells like a mix of oil and gasoline.

Does the odor ever go away on its own? Or is there something that I
might
use to get it out?

I would be worried about breathing benzene, ethylbenzene, toluene and
xylenes - all cause cancer. Get it professionally cleaned, replace the
carpet, or I would recommend the match solution.
Good luck,
David