One of my big rig drivers is claiming he's seeing a 1 mpg increase OTR (500 Cat). I'm always willing to give anything a try, but it's a limited availability (only a few retailers) or mail order only. The price is steep, but when computing out recommended ratios seems no more expensive than other additives. It appears that this additive is purely for a mileage boost, and does nothing for gelling or water.
http://www.ca40g.com/home.php
http://www.ca40g.com/home.php