CA-40 has been advertised heavily here in the upper midwest partly as a gas saver. I finally tried some this past summer. I followed the mixing instructions and tried it in our two cars, each which have a digital MPG gauge. I also used it in my motorcycle which I commuted to work on. I used it for two tank fulls in each vehicle. I found no difference in fuel mileage, much less the 10% increase the advertisements promised. The company has a money back guarantee, and they did refund my money ($30.00) no questions asked, so I've got to credit them for that much. The company did claim they had a bad batch produced last summer, and they blamed the problem on that.