The easiest way is to consult your vehicle’s instruction manual to determine what fuel your vehicle manufacturer recommends. Frankly, some cars will run better with premium, while others simply will not. Here is how you can figure out what’s best for your car:
Check the owner’s manual: Dig out your old manual and find the section regarding fuel. It should tell you all about what’s best for your engine.
Take a test drive: If your vehicle uses Regular Unleaded gas, there’s no harm in testing how it reacts to Premium fuel. Drive your car with premium gas and then regular unleaded. Compare how it runs given the fuel difference, then you can determine whether the performance of your vehicle outweighs the cost difference.
Pay attention to how you use your car: Vehicles encountering frequent rugged terrain or use will perform better with premium gas because the fuel is more resistant to combustion and pinging.
Here's why premium fuel may not always be better though: http://www.motorist.sg/article/96/95-vs-98-petrol-are-you-actually-wasting-money-on-premium-petrol