I recently began driving a car that had traditionally used premium gas (93 octane). According to the maker, though, it requires only 91 octane. The thing is, in the US, you can buy only 87, 89, or 93 octane. Where I live, gas prices jump 30 cents per gallon jump from one grade to the next, so premium costs 60 cents more than regular. So why not try to save some money?