Premium gas has a higher octane rating. Octane rating measures a fuel's resistance to knocking (pre-ignition). Cars that require premium gas have engines designed to take advantage of that higher resistance to prevent knocking at high compression ratios. A car designed for regular unleaded doesn't need that higher octane, and the extra expense is wasted. You won't get any extra power or better fuel economy. You're simply paying more for fuel that offers no additional advantages in your vehicle.
