These days it seems that everyone is talking about fuel, but how much do you really know about that mysterious liquid that gets your car from point A to point B? Here are a few answers to some common questions.

What does “unleaded” mean? Is leaded fuel still around?

Lead, specifically tetraethyl lead, was originally added to gasoline to boost octane ratings. However, it was later determined there were damaging health effects from the use of leaded gasoline and its use was discontinued in the U.S. in the 1970s. The lead additive was replaced by ethanol (grain alcohol) additives, which provide the same anti-knock benefits as lead but without harmful side effects. Leaded fuel is still allowed in the U.S. for aviation use only.

What is an “octane rating” and how do I know what type of octane to use for my car?

An octane rating, also known as the anti-knock index, is the measurement of a gasoline’s ability to restrict engine knock – a rattling or pinging sound that results from uncontrolled combustion in the engine. Engine knock can cause overheating and damage to your engine over time.

It’s commonly believed that higher octane ratings represent more power, but that’s not the case. Different cars require different levels of octane so be sure to check your car’s owner’s manual for the manufacturer’s recommendation.The most common levels of octane are 87 (regular), 89 (mid-grade), and 93 (premium).

Does it matter what brand of fuel I buy?

Many people think “gasoline is gasoline” but that’s simply not true. While the base fuel that comes from the refinery may be similar, branded gasolines are different because of the proprietary additive that’s included in them.

For example, Shell additive technology is proprietary and is used exclusively in all grades of Shell gasoline. Shell regular and mid-grade gasolines contain more than two times the minimum amount of cleaning agents specified by the Environmental Protection Agency (EPA). Tests prove that Shell gasolines can help vehicles avoid the build-up of “engine gunk” (or carbon deposits) more effectively than gasolines containing only the minimum amount of cleaning agents required by the EPA. And Shell V-Power®, Shell’s premium grade gasoline, can clean up the gunk left by low-quality discount gasolines. All Shell gasolines meet the TOP TIER Detergent Gasoline Standard established by top car manufacturers.

Now why does this matter? Engines work most effectively when they have the precise mixture of air and gasoline to burn. Gunky build-up can reduce an engine’s ability to breathe, which can keep a vehicle from performing as the manufacturer intended.

What is the difference between diesel fuel and regular fuel?

Diesel fuel and regular fuel come from the same place - crude oil. However, just as grape juice and wine come from the same source, the end results are quite different. In addition to the chemical makeup of gasoline and diesel being different, diesel fuel is less refined and more “heavy” than gasoline. This partially accounts for the higher mileage that diesel-powered cars can achieve. While diesel engines have been unpopular among American motorists due to their noise and odorous exhaust, modern diesel engines are now becoming just as quiet and clean burning as gasoline engines.

For more information on gasoline and tips to get the most out of every tank, visit www.shell.com//fuel_facts/ and www.shell.com/shell_for_motorists/fuels/fuel_stretch/.