Ive tried it a few times, nothing really noticeable. I do see on my fuelly app that I ran it twice in a row and noticed a .1 and .2 mpg increase, and dropped back down again after Sunoco, but could have been driving habits over those tanks, no warmups etc. Some stations are pricing it fairly, 2.95-2.99, which Ill use, and some show 3.49+. One maniac is 3.89 on a busy highway, I guess hoping people wont pay attention?