100LE AvGas, no additives needed, I drain the carb after use and put the generator away till I need it again. I have left it unused for 6+ months and the only problem is you have to slow pull the starter rope a dozen or so times to prime everything before you do a couple of serious pulls to start it. Gas is not cheap but I don't use that much. I keep about 15 gallons on hand and run it in my other small engines and replenish as needed. Shelf life on Av gas is 3+ years according to the manager of a small airport I use to buy from.