Current recommendations are to use a minimum of 87 octane, 89 octane is preferred. There is no additional benefit from using higher-octane fuels, in fact they may cause hard starting conditions in hot weather. If you have an older motor and the owner's manual requires premium fuel, here's why: When these were built, the best oil available was TCW-2 rated, and did not contain the additive package (detergents, carbon preservatives, etc.) which our current oils (XD-30, XD-50 and XD-100) contain today. In that era, premium fuel contained the additive package that helped prevent the formation of internal engine deposits. That's why premium fuels were preferred at the time. Ultimately, in the late 90's the federal government mandated fuel refiners to use the same additive package in all grades of fuel and the premium fuel requirement was dropped.