When deciding between the various grades of gasoline at the pump-most commonly regular, mid-grade and premium-something to consider is octane level. Different grades of gasoline usually have different levels of octane that can range from 87 to 93, so it's important to check your owner's manual to know which one is right for your car. Octane is a fuel's ability to resist overheating, which can lead to engine knock-a rattling or "pinging" sound under the hood. Using the appropriate level of octane can prevent this and ensure proper fuel combustion in your engine.

Although most cars will function with a lower octane level, they may not operate as the manufacturer intended. For instance, I work with top-of-the-line BMWs every day, and a modern BMW engine-management system can automatically compensate for a fuel with lower octane levels. But just because these BMWs can compensate for lower octane fuel doesn't mean they will perform at their top level.

While most people associate high octane levels with high quality, it's really not an appropriate comparison. Outside of octane considerations, cleaning agents play a large role in the makeup of a fuel.

Cleaning Agents

Back in the '80s, fuel would leave a tarlike deposit on engine parts and cause a car to stumble. Eventually, the Environmental Protection Agency (EPA) stepped in and established a set of minimum standards for cleaning agents to be added to gasoline. And while fuel technology has advanced over the last 20 years, most gasolines contain only the minimum amount of cleaning agents required by federal government standards, which can still leave carbon deposits on critical engine parts.

Now, why is this important? The simple answer is that carbon deposits can restrict the amount of air and fuel that get drawn into the engine and prevent your vehicle from operating as efficiently as the manufacturer intended. And in my experience, carbon deposit buildup can only worsen a car's performance and fuel economy.

Four leading automotive manufacturers-BMW, General Motors, Honda and Toyota-became so concerned with declining gasoline quality that they introduced a higher standard called the Top Tier Detergent Gasoline standard. Top Tier fuels surpass government standards and can help prevent deposit buildup on critical engine parts, such as intake valves and fuel injectors.

To avoid carbon deposits, consumers should look for a high-quality fuel that meets the Top Tier standard. In fact, I always recommend my customers use a premium fuel with added cleaning power to help get the most out of their vehicle. For example, Shell claims its premium fuel, Shell V-Power, can actually clean your engine as you drive and help reverse the effects of carbon deposit buildup.

The Wise Choice

The bottom line is that your car will most likely function no matter what grade of gasoline you purchase-the question is how well and for how long. Buy what's right for your car. While laying out the money for premium gas may seem like an extravagance, in the long run, using high-quality fuels with added cleaning power will benefit your car and enhance your driving experience.

• Steve Dinan has been rebuilding and modifying cars for 38 years-including 27 years as the head of Dinan Engineering, the premier BMW tuning company in North America. Over that time, he's spent thousands of hours working to extract the maximum performance out of BMW engines. Steve Dinan is a spokesman for Shell Oil Products U.S