Filling up at the gas station is an expensive way to spend a few minutes. As the cost of gasoline continues to fluctuate, drivers want to get the most bang for their buck at the pump. Understanding octane and which one is appropriate for certain cars can save drivers substantial amounts of money.

When vacillating between whether to choose premium or regular, it pays to read your owner's manual and it can't hurt to learn a little about the chemistry of gasoline.

Gasoline is the fuel for your car. It is available in 87 octane (regular), 89 octane (plus) and 91 octane (premium) in most areas. Regardless of fuel grade, the three major octane levels at the pump offer the same amount of heat energy, say automotive experts. What determines the differences in gas is the propensity for the gasoline to cause a ping or knock. This occurs when an uncontrolled burn or an explosion of the fuel takes place in the engine. Typically, this happens when part of the fuel-air mixture in one or more of the car's cylinders ignites spontaneously due to compression.

Higher performance cars require more engine compression to generate more horsepower. Therefore, putting regular gasoline in these types of vehicles may exacerbate knocking and pinging issues. Premium, high-octane fuel is specially designed to burn more slowly than regular, reducing the chances for those small explosions in the engine.

Some people are under the impression that premium fuel offers other benefits, such as it contains more detergents to help clean the engine during use. This is inaccurate, and the U.S. government requires a certain level of detergent in all grades of gasoline. Despite these untruths, some people are insistent upon paying $.20 to $.30 more a gallon to fuel up with a higher grade of gas.

Typically the higher the price of the car, the greater propensity it will "require" premium gas. Automakers use premium fuel to distinguish their higher-market models. For example, most Toyota models can run on regular, while the Lexus line suggests premium. The same can be said for Honda/Acura models. Premium gasoline garners a higher profit margin for gasoline retailers and refiners, so there is a definite advantage for them working in cahoots with automakers to push premium gas.

While premium gas may reduce some knock and ping in high-performance engines when they are pushed, in most cases vehicle owners will be hard-pressed to tell the difference in performance when filling up with regular or premium. According to fuel specialists at General Motors, the only modern engines that should really need premium are those with superchargers, which force-feed fuel into the cylinders. In fact, drivers of cars that require regular who routinely fill up with premium gas could be doing their engine a disservice. The higher density of premium gasolines could lead to a buildup of waste products inside the engine over time.

The Federal Trade Commission has even issued a consumer notice in the past, stating: "In most cases, using a higher-octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage, or run cleaner."

The bottom line: Vehicle owners should read the car manual that comes with the auto. Stick to the recommended octane level, and the car should perform as indicated. If a car requires premium fuel, experiment with mid-grade to see if knocking occurs or if there is any apparent decrease in performance. If not, enjoy the extra savings at the pump.