I claim a bit of insider industry information about gasoline additives, having engineered and installed 40 additive injection systems at distribution terminals. I've heard all the horror stories and success stories. First, additives do nothing to alter octane rating. Don't waste your money unless it makes you feel good. Second, if you buy gasoline from busy major retailers and don't age it for too long before you burn it, water accumulation in your vehicle is not a problem. There was a time in the 80's when there were no additives in generic gasoline and everyone got by just fine. The Federal Trade Commission made distributors put in additives for generic gasoline just in case a rash of water accumulation happened. Third, the proprietary formulas for additives make very little difference in what little good they do. A tiny spritz of light machine oil in a gas tank will bind up what little water may accumulate. You would be amazed at how little gasoline additive is put in tanker trucks for delivery to retailers. I won't name the major oil company, but I saw their additive manufacturing unit. A few solvents and liquified animal fat went in the witch's brew. For whatever good it did, it worked for decades. As several have noted above, direct injection engines derive little benefit from additized fuel. The additive gets incinerated and does nothing for exhaust valves. Clean, high quality motor gasoline with low contaminants works the best for this. If you are really fussy about clean fuel, simply buy premium grade, not for the octane rating, but to avoid the fuel transfer errors in the distribution system that push mistakes into the lowest grade fuel. You would be amazed at what ends up in regular gasoline.