Using 91-octane premium fuel instead of 87-octane regular fuel will only increase your engine's power if your car's manufacturer specifically designed the engine to require it.
Higher octane fuel resists knocking or 'pinging' under compression, which is a premature ignition of the fuel-air mixture. Engines designed for higher octane can take advantage of this resistance to operate at higher compression ratios or with more advanced timing, which can lead to increased horsepower and efficiency. However, if your vehicle's owner's manual specifies regular 87-octane fuel, using premium 91-octane will likely offer no discernible performance benefit and is generally not recommended. Always consult your vehicle's manual for the correct fuel grade.
Fuel octane requirements are determined by the vehicle manufacturer and using a higher octane than recommended typically provides no benefit.
Is it ever worth paying extra for premium gasoline?
Paying extra for premium gasoline is only worth it if your vehicle's manufacturer specifically recommends or requires it for optimal performance and engine health. This is typically the case for high-performance engines, turbocharged or supercharged vehicles, and some luxury cars designed with higher compression ratios. For these vehicles, using premium fuel prevents knocking, allows the engine to operate at its designed power output, and can maintain expected fuel efficiency. For any vehicle designed for regular 87 octane, the extra cost of premium gas offers no tangible benefits.