Check your owner’s manual to find out what fuel octane rating your car's engine needs then buy it. Resist the urge to buy higher-octane gas for “premium” performance, unless your car requires it. Octane has nothing to do with the gasoline’s performance, merely its volatility factor in the combustion chamber. Why do high-performance vehicles need higher-octane fuel? Because the combustion chamber environment is much hotter in the performance engine. Using high-octane fuel reduces pre-ignition in the upper regions of the combustion chamber, which can damage valves and pistons if allowed to go for long periods of time. Experts from the Automobile Association of America (AAA) say that about five percent of the cars sold in the U.S. require premium gasoline. Yet premium gas accounts for 20 percent of all gasoline sold. Check your owner’s manual for the recommended octane rating and stick to it.