Well just did an entire read through of my manual last night before bed. It just so happens the owner manual's recommended octane rating is 91! I fill up with premium 93 always. However sometimes the plus can be 90 or 91. But often times its only 89 depending on the gas company. Anyways as previously stated the difference in price is so insignificant its worth it. Think of it as if you were buying something for your kid, you want the best of everything right? In order to keep them happy and healthy!