Generally speaking you'll get slightly higher mileage with higher octanes, but it's hardly worth the extra cost.O-wood said:I agree, higher octane only increases performance not decrease emmisions. California gas has some additives to it too. Guess that's why it's more expensive here than in any other state. I also wondered if higher octane gives you better gas milage. I get 26mpg in combined driving, wonder what I'll get with 93 or 94.