Product FAQs

What is meant by TOP TIER gasoline?

TOP TIER is a standard of gasoline that contains higher levels of detergent additives than current Environmental Protection Agency (EPA) standards. The EPA requires that all gasoline marketed in the United States contain detergents, which are added to gasoline to help clean fuel injectors, intake valves and other engine parts.* The TOP TIER standard is set by a governing body of several automakers and is recommended in their vehicles’ owner manuals. Exxon and Mobil gasoline contains significantly more detergents than the minimum quantity required by the EPA and has passed other performance tests, such as deposit control on intake valves and fuel injectors, resulting in it being certified TOP TIER.

What is the difference between gasoline and diesel?

While diesel and gasoline are both derived from crude oil, they work in two different ways and are not interchangeable. Diesel fuel is designed to operate in a diesel engine, where it is injected into high-temperature air and ignites spontaneously under compression. This differs from gasoline, which is ignited by the spark plugs in a gasoline engine. It is essential that you put the right type of fuel in your vehicle.

What steps do you take to ensure the quality of your fuels?

We have stringent quality control procedures and active quality monitoring programs to help protect our fuels from manufacture through to distribution. Tests are conducted on the fuel at the refinery to ensure that it meets or exceeds engine manufacturer and industry specifications. Our additives are accurately injected as each delivery truck is filled at the terminal, ensuring the quality of our fuel and providing additional benefits. Finally, all of our service station gasoline dispensers have built-in filters to provide a final cleaning as the gasoline enters your vehicle tank.

What kind of fuel should I use in my lawnmower/garden equipment?

Generally, regular gasoline will be fine. If the engine is 2-cycle (as commonly found for chain saws or edge trimmers), then 2-cycle oil will be required in the fuel. Consult your owner’s manual for a recommendation.

Why should I use Exxon or Mobil branded fuel every time I fill up?

When you purchase gasoline at an Exxon- or Mobil-branded, you’re fueling with advanced Synergy gasoline. Engineered with 7 key ingredients to help you get better gas mileage,** Synergy gasolines provide lower emissions and improved engine responsiveness** and are designed to provide corrosion protection and improved performance compared with gasolines meeting minimum government detergency standards. In addition, Exxon and Mobil Synergy™ gasoline contains significantly higher detergent levels than EPA requirements and has passed a series of deposit control performance tests, resulting in it being certified TOP TIER®.
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Does gasoline really need detergents?

Yes! Detergents are added to gasoline to help clean vital engine parts, including fuel injectors and intake valves. While the EPA has mandated that all gasoline marketed in the United States contains detergents since 1995, our gasoline contains significantly more than the minimum quantities required. In fact, Synergy gasolines contain two detergents, one that’s a lot like a household detergent, helping to remove any harmful deposit buildup and one that targets the toughest gunk. When combined, these detergents work to improve fuel economy.**

What is unleaded vs. leaded gasoline?

If you filled your tank prior to the 1990's, you might remember that there were two choices of gasoline: "regular" and "unleaded." At the time, "regular" gasoline contained tetraethyl lead, which served as an octane booster in fuel. All vehicles manufactured after 1975 are built with catalytic converters and require unleaded gasoline. Catalytic converters help convert pollutants in exhaust to less toxic gasses such as carbon dioxide, nitrogen, and water vapor. Due to environmental concerns, leaded gasoline was phased out in the 1990’s and can no longer be sold at any gas station in the United States. Today, "regular gas" no longer refers to gasoline with lead content, but rather to a certain grade of unleaded gasoline.

How is gasoline performance determined?

The performance of gasoline is determined by multiple factors, including its antiknock quality (also known as octane rating), its volatility, and its detergency. Check your owner’s manual to see what octane rating is right for your vehicle.

What does antiknock mean?

Antiknock, also known as octane rating, is a measure of the gasoline's ability to resist knocking or pinging during combustion. Since it is gasoline vapor rather than liquid fuel that ignites, the air-to-fuel mixture must be correct for smooth combustion. The higher the octane rating, the greater the engine's resistance to knock. Some of the problems associated with knock are overheating of critical engine parts – namely valves, pistons and spark plugs. To minimize the effects of knocking, modern engines are equipped with knock sensors, which temporarily delay the spark timing in the piston’s compression cycle. While this prevents audible knocking, delaying the ignition spark also sacrifices engine efficiency.

What does volatility mean?

Volatility refers to a series of characteristics that measure a fuel’s tendency to vaporize at a given temperature. Since gasoline must vaporize before mixing and burning with air, formulating fuel with the correct volatility is critical for achieving good drivability. High volatility gasoline vaporizes more readily than low volatility fuel and is frequently blended during the winter season to ensure easy cold startup and smooth warm up. In hot weather, gasoline that is too volatile can cause vapor lock and other hot fuel handling problems. Exxon and Mobil gasoline is carefully formulated on a seasonal and geographic basis to provide the correct vaporization characteristics for proper vehicle operation.

What does detergency mean?

Detergency is the performance characteristic of a gasoline that refers to its ability to clean and protect the fuel delivery system, including the carburetor or fuel injectors, and intake valves. A gasoline detergent is fundamentally like a household detergent. It is a molecule that affixes itself to dirt particles. As gasoline passes through a car's engine, the molecule helps clean away dirt particles and helps to prevent any harmful deposit build-up.

Why do diesel engines sometimes emit smoke?

A modern diesel engine is calibrated to inject the amount of fuel necessary to complete combustion across a range of power outputs. White smoke can be temporarily present during startup, particularly in wintertime, as unburnt fuel mixes with exhaust. The presence of black sooty smoke is an indication of mechanical problems resulting in incomplete combustion. More specifically, sooty particulates are generated with non-ideal atomization of diesel fuel resulting in a fuel-rich combustion atmosphere. Newer vehicles equipped with diesel particulate filters greatly reduce the presence of this smoke.

What does “Ignition quality” mean and how is it determined?

Ignition quality relates to a diesel fuel’s cetane number – a measure of how readily the fuel auto-ignites under compression in the engine’s cylinder. In the United States, the minimum cetane number requirement is 40, which ensures good ignition quality, ease of start-up, and smoothness of operation in modern diesel engines.

How do lower temperatures impact the operability of diesel fuel?

Low temperature operability is the ability of the fuel to flow through the vehicle’s fuel system without plugging filters at low temperatures. Since diesel fuel contains paraffin waxes that may become solid at colder ambient temperatures, the cold flow properties of diesel fuel can be estimated with filterability tests and by measuring the cloud point temperature. To help address this problem, modern diesel engines are designed to warm the fuel pump and filter with engine heat.

What are some of the causes of poor diesel engine performance?

Fuel contamination by water and dirt may cause poor diesel engine performance. Extreme care must be exercised when storing and handling fuel. Fuel-tank caps, dispensing nozzles, and hoses should be kept clean to eliminate potential sources of contamination. Fuel injectors and pumps are especially sensitive to wear and abrasion from particulate matter in fuel. Regularly removing water from storage tanks, vehicle fuel tanks, and filter bowls is important. Dry storage systems help reduce fuel emulsion problems, injection system corrosion, and microbial growth.

Can I store diesel and for how long?

If you keep it clean, cool and dry, diesel fuel can be stored for six months without significant quality degradation.

Will gasoline with ethanol affect my vehicle’s fuel efficiency?

Ethanol contains less energy than gasoline per gallon of fuel, but any changes in the fuel economy performance of your vehicle are expected to be minimal.

If I have water in my vehicle’s fuel system can I use ethanol-blended fuel?

Water in your vehicle’s fuel system may cause problems regardless of whether ethanol is present or not. A number of products are available to remove water from your fuel system. You should consult your mechanic for a recommendation.

Will my vehicle require additional maintenance?

Regular vehicle maintenance is always recommended, regardless of fuel type. Gasoline containing up to 10% ethanol is suitable for use in most vehicles and will not require additional maintenance.

Is there a situation where my vehicle’s octane needs would differ from the level recommended in my owner’s manual?

In general, the octane needs of a vehicle align with the manufacturer’s recommendation. However, a small percentage of vehicles may require higher octane fuel under certain conditions. Extremely hot weather, changes in altitude, or exceptionally hard driving conditions, such as towing heavy loads, may cause knocking. Additionally, knocking may be the result of slight variations in engine construction variability or unusual engine deposit build-up. Many modern vehicles are equipped with electronic knock sensors that detect and eliminate light knocking before you hear it.

Why do gasoline prices fluctuate?

The major factor in fluctuating gasoline prices is the price of crude oil, which is continually impacted by supply and demand. Crude oil impacts the price of gasoline just like other commodities such as corn, coffee and cotton, impact the price of goods. For example, a shortage of corn crops could cause the price of some foods to increase.

Why do gasoline prices differ between companies?

Even though all oil companies sell gasoline products, those products are not identical. Different manufacturers use different techniques and unique formulas in the refining process that may impact prices. As well, where and how a gas company sources their crude oil will impact prices at the pump.

What are some ways I can save at the pump?

Be sure to check out our Fuel Efficiency Tips to learn about some of the ways you can improve fuel efficiency and save at the pump. You can also apply for the ExxonMobil Smart Card, which lets you save on fuel purchases.