Actually tested this in a semi controlled environment. 2002 VW Jetta. 4 holer. 23K miles. DTW (Detroit Metro Airport) to ORD (Chicago O'Hare). Without 27.4 mpg. With 29.3 MPG. New Plugs, Oil, Oil and air filters before 1st trip/test. Same car, same miles, same driver, same load, even real close to the same temp out, there and back. 1.9 mpg increase. Mixture: 1 oz to 6 gallons. Terry Bogusz GSE Manager Spitit Airlines Detroit Metro Airport