I did a search of the forum and didn't find anything on the subject.
I was watching Jay Leno's Garage and found this video:
Apparently, Archoil is an American-Based company and their products work well if Amazon reviews are of good indication. They make friction modifiers, a rust remover and a fuel treatment. A quarter ounce of the treatment treats 20 gallons of gas.
http://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=archoil
So, you tell me... Have you tried this to increase your MPGs? If so, how does it work?