Gasoline FAQ

gas faq

Other than price, what is the difference between regular, midgrade, and premium gasoline?
Gasolines are rated based on octane. In most areas of the country our regular gasoline is 87 octane, midgrade is 89 and premium is 91 – 93. If you check your owner’s manual, you’ll find the recommended level for your engine.

Why should I follow my owner’s manual and choose mid or high-octane fuel? Isn’t gas just gas?
To get the best performance out of your vehicle, you should use the octane recommended in your owner’s manual. Most vehicles do not benefit from a higher octane level than what is recommended but using a lower octane than recommended can cause engine knocking or pinging in some cars.

Does gas have an expiration date?
In general, gasoline should be used within a month of purchase. When the engine will not be used for an extended period of time, it’s best to drain the fuel tank and then run the engine until it stalls. If you choose to store gasoline, keep it in a very nearly full, tightly sealed metal container in a cool environment. Be sure to leave some room in the container to allow for some expansion. Under these conditions, the gasoline can be expected to remain of good quality for at least six months.

Is there a situation where the octane my vehicle needs would differ from the level recommended in my owner’s manual?
In general, the octane a vehicle needs aligns with the manufacturer’s recommendation. However, each vehicle is different, owing to factors such as manufacturing variability, mileage, type of operation and general condition. As a result, some vehicles may require a higher octane, particularly after an initial period of operation.  If knocking or pinging suddenly occurs, using a higher octane grade may resolve the problem.

 What kind of gas should I use in my lawnmower/garden equipment?
Consult your owner’s manual for a recommendation. 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 may also be required in the fuel.  This will be explained in the owner’s manual.

Who decides how much gas is going to cost?
In most countries with free markets, service station operators — many of whom are independent business people — set retail pump prices. The supplier typically sells the station owner gasoline at a wholesale price reflecting prevailing market conditions. The station operator then decides what price he will charge the public.

When supply exceeds demand, service stations will lower prices to compete with each other for business. When demand exceeds supply, service stations raise prices to prevent run-outs. Higher prices encourage station owners and suppliers to seek additional supplies. This competition generally rebalances supply and demand quickly with minimal disruption to consumers.

What should I do if the gas gets on my car or myself? / How do I get the smell of fuel off my hands?
Gasoline on your vehicle can be wiped away with a rag or paper towel.  Washing with soap and water will typically remove any odor from your hands, but if the scent lingers, try mixing vanilla extract with water and rubbing it on your hands until the mixture reduces or removes the smell. You can also use rubbing alcohol or lemon juice. Once gasoline smell is gone, wash your hands with soap and water once more to avoid any stickiness.

Why should I use Exxon or Mobil fuels?
Because you can be assured that whenever or wherever you buy the fuel it has met the high quality standards that ExxonMobil applies from manufacture through distribution, all the way to you, the final consumer.   

Will mixing gas from one manufacturer to another cause a problem with my car?
While we are completely certain about the quality of ExxonMobil fuels, we cannot provide any assurance about the quality from other suppliers.

Why should I use your premium gasoline (91-93 octane) instead of regular (87) or midgrade (89)?
To find out what octane your engine needs, first check your owner's manual. The recommended level is often 87 octane. Some models have high compression engines which are designed to utilize the octane levels of 89, 91 or higher.

Ordinarily, your vehicle will not benefit from using a higher octane than is recommended in the owner's manual. But if your engine knocks or pings at the recommended octane level, you may need a higher octane gasoline to prevent the knock. Knocking may occur under certain conditions. A small percentage of vehicles may knock because of variations in engines of the same model due to manufacturing tolerances, or because of an unusual build-up of engine deposits. Other factors such as extremely hot weather, changes in altitude or hard driving conditions (like towing a heavy load) may also cause knocking. Many modern vehicles are equipped with an electronic device that detects and eliminates light knocking before you hear it.

What is reformulated gasoline?
Reformulated gasoline (RFG) is a special blend designed to reduce harmful automotive emissions. RFG must be marketed in those areas of the United States where air quality doesn't meet the ozone requirements of the Clean Air Act Amendments. It is formulated to reduce the emissions of NOx and volatile organic compounds, and has lower benzene levels.

For more information on RFG, visit the API's web site.

What is California Air Resources Board (CARB) gasoline?
CARB gasoline is a type of reformulated gasoline designed to reduce emissions. It reduces the emissions of NOx and volatile organic compounds, has lower benzene and sulfur levels, and limits the amounts of aromatic and olefinic compounds in the blends. It is required throughout the state of California.

For more information on CARB gasoline, visit the California Air Resources Board website.

Do your gasolines contain MTBE?
ExxonMobil does not use MTBE in our gasolines in the United States.

Do your gasolines contain ethanol?
In many areas of the country, oxygenates are required to be part of the gasoline formula. In those areas, our gasolines will contain ethanol, which is an oxygenate [US Fuel Requirements Map]. Ethanol is also used in California Cleaner Burning Gasoline and the Reformulated gasolines required in many of the major metropolitan areas of the country.  In addition, to meet the Renewable Fuels Standard included as part of the Energy Independence and Security Act of 2007, ethanol blends have been introduced to many more areas of the country.

Do your gasolines contain methanol?
Methanol is not used in our gasolines.

Do your gasolines contain MMT?
In the United States, our gasolines do not contain MMT.

Do your gasolines meet the Worldwide Fuel Charter?
The World-Wide charter, formerly known as the AAMA Gasoline Specification, has been proposed by many of the automobile manufacturers. To this point, however, the need for the more costly fuel has not been adequately demonstrated, so the specifications have not been adopted by ASTM where auto/oil/consumer consensus specifications are developed. Our gasolines meet ASTM D4814, Standard Specification for Automotive Spark-Ignition Engine Fuel, as well as all federal, state and local legal requirements. Use of our gasolines will not void your vehicle’s manufacturers' warranties.

Do your gasolines contain detergents?
All our gasolines contain effective detergent additives. While the EPA has required all gasolines marketed in the United States to contain detergents since 1995, our gasolines contain significantly more than the minimum quantities required to provide additional protection against fuel system deposits.

Does gasoline really need detergents?
Yes! Detergents are added to gasoline to help keep vital engine parts clean, including the carburetor or fuel injectors, intake valves and intake port areas. A gasoline detergent is a lot like a household detergent, helping to prevent any harmful deposit buildup.

Gasoline detergents can do such a great job at keeping critical engine components clean that the Environmental Protection Agency (EPA), through the Clean Air Act, has required them to be added to all gasolines since 1995.

What steps do you take to ensure the quality of your fuels?
We have stringent quality control procedures to help protect our fuels at every step of the process.

  • Tests are conducted on the fuel at the refinery to ensure that it meets or exceeds engine builder and industry specifications.
  • Our additives are precisely injected as each delivery truck is filled at the terminal, guaranteeing that the gasoline will meet all performance standards and provide additional benefits to you, our customer.
  • At the service station, delivery drivers and retailers check it once more to ensure that it hasn't become contaminated with water.  In addition, all of our gasoline dispensers have filters to provide a final cleaning just before the gasoline enters your vehicle tank.

And we don't stop there. Once our fuels have been delivered, we survey them at our stations to confirm that

  • Our Reformulated gasolines meet all federal standards.
  • Our gasolines meet state and other locally specified limits.
  • Our gasolines contain the proper type and amount of our detergent additives.

What is the importance of a gasoline’s antiknock quality?
Antiknock, also known as octane rating, is the measure of a gasoline's ability to resist knock or ping during combustion. The higher the octane rating, the greater the engine's resistance to knock or ping. The knocking or pinging in your engine occurs when the air/fuel mixture detonates prematurely. Since it is the gasoline vapor that ignites, the air/fuel mixture must be correct to burn smoothly. Some of the problems associated with knock are overheating of engine parts such as valves, pistons and spark plugs.

Car manufacturers will specify, in the owner's manual, a minimum octane to be used with their automobiles. Ordinarily, your vehicle will not benefit from using a higher octane than is recommended in the owner’s manual.

But if your engine knocks or pings at the recommended octane level, you may need a higher octane gasoline to prevent the knock.

What does a gasoline’s volatility mean to me?
Volatility is the rate at which gasoline vaporizes at a given temperature. The volatility of a gasoline is important because the liquid gasoline must be mixed with air and vaporized in order to burn in the engine.

The volatility characteristics of our gasolines are important to your driving performance. Gasoline with high volatility vaporizes more readily than one with low volatility. In hot weather, gasoline that is too volatile can cause vapor lock and stalling in your vehicle. In cold weather, a gasoline that is not volatile enough may cause hard starting and poor warm-up. In the winter months, for example, your vehicle's engine is extremely cold before startup, and the gasoline must have a high enough volatility to be able to vaporize easily in a cold engine environment. Our gasoline’s volatility is carefully balanced on a seasonal and geographic basis, to provide the correct vaporization characteristics to ensure proper operation in your vehicle.

Do your gasolines meet U.S. emissions standards?
Absolutely. Our gasolines meet all federal and state requirements applicable in the areas where they're marketed.

In 1963 Congress passed the Clean Air Act, which set in motion a series of changes to automobile design and fuel formulations. Initial changes occurred to engine designs, but in the 70s, fuels were impacted by the requirement to remove lead antiknock compounds. Other changes have followed, notably the requirement to have oxygenated gasolines in carbon monoxide non-attainment regions in the early 90s and reformulated gasolines in severe non-attainment areas in the mid-90s.

In addition to these federally mandated changes, many states have also required changes to the fuels. The impact of all these changes has been improvements in air quality - even while the miles driven have increased substantially.