Many older vehicles have steel gas tanks, that if you only fill it halfway, the ethanol in the gas will condense on the sides and top of the tank, eventually pitting the tank, creating a hole.

Added ethanol is the standard in gasoline now, for all grades. There is a requirement to state that it doesn't have ethanol in it. So, if your local gas station doesn't have a sticker on the pump stating that there is 10% ethanol in it, don't worry it's all there.

Recreational fuel is recommended for all small engines, especially chainsaws. And don't forget to add the special oil additive to chainsaw gas. Even pour a little out to make certain that it has the blue dye in it, or purchase the Motofuel by Stihl, it's made with 95% paraffin gasoline. It has so much paraffin in it that you can smell it when you run your saw. The exhaust gasses will smell like candle wax. It's pricey, but replacing the saw is more expensive than the fuel you run in it.