Just finished the second tank of Mobil Premium (after two tanks of Citgo Prmium) and as others have said, there was no increase in mileage or performance. My mileage was within 1/2 mpg using premium or regular. I'm going to stick with the regular and save the money.

 

You are so right buddy

**I own a 2000 Civic Si and my Friends dad has his own Honda shop and told me stick with JUST premium on your car. No exceptions** [&:]

 

with Si's yes it's premium... however, the others take regular... using a higher grade once in awhile isn't too bad, but if it's used too much it can potentially hurt the engine. the higher the grade, the more "cleaner" it is... and that can wear out the insides of the engine.

and with the price of gas now (over $4 for 91 octane), it's probably better for your wallet if you just stuck with regular.