why do a bunch of gas stations have 88 octane cheaper than 87?
I figured it was a marketing gimmick to get you to buy 88 and then they would finally raise the price, but it's been years. are they adding extra ethanol or something?
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That cheaper 88 octane fuel is a blend of 85% unleaded gasoline and 15% ethanol. It's also known as E15 fuel.
The ethanol is an oxygenate: it adds oxygen atoms to the fuel mix so the fuel burns more completely. That's good for vehicle emissions. However, the ethanol is less energy dense than gasoline so you will get slightly worse mileage.
https://www.motortrend.com/news/what-is-e15-gasoline-pros-cons/
https://www.cleveland.com/news/2023/05/cheap-gas-lower-mpg-are-unleaded-88-and-flex-fuel-more-expensive-in-the-long-run-saving-you-money.html