Skip To Content

Fuels FAQs

Take a deeper dive into other questions about our fuels.

Fuels FAQs

Common questions about our fuels.

In general, gasoline is a complex mixture of many components, called hydrocarbons, which are refined from crude oil. These hydrocarbons are blended together to produce a fuel that’s used to power spark ignition, internal combustion engines. The recipe used for blending these hydrocarbons may vary from refinery to refinery. Finished gasolines, however, are required to meet certain specifications as defined by federal and state regulations and ASTM International.

Formerly known as the American Society for Testing and Materials, ASTM is one of the largest voluntary standards developing organizations in the world. The volunteer members represent producers, users, consumers, government, and academia from more than 140 countries. They develop technical documents that are the basis of manufacturing, management, procurement, codes and regulations for dozens of industry sectors including petroleum fuels.

It means that our gasoline complies with rigorous standards developed through an independent industry organization whose focus is to ensure that products achieve what they are designed to do. Some of the best technical minds in the industry participate in ASTM International and influence the way that products are defined as fit for purpose.

For your car, it means that gasoline conforming to ASTM International standards, like CITGO TriCLEAN gasoline, should provide reliable service for your transportation needs. Gasoline that does not meet the ASTM standard could result in unsatisfactory performance.

CITGO owns and operates bulk storage facilities, also known as terminals, which receive and store fuel prior to its transport to gasoline stations. At these CITGO-controlled terminals, there are ongoing and established programs designed to monitor product quality. For example, our routine oversight includes checking fuels prior to distribution to gasoline stations to determine whether the fuel has changed in transit, possibly rendering it “unfit” or “unsuitable.” Any fuel not in compliance with our standards is isolated within our system. To further ensure product quality, samples of the products in storage are routinely collected and sent to the CITGO quality monitoring laboratory for testing and verification for compliance to standards. These test results are reviewed by fuels technical specialists who discontinue distribution of any product that does not comply with CITGO standards.

In addition to the terminals, CITGO has established programs to monitor product quality at all of our branded gasoline locations. The test results are reviewed by fuels technical specialists for compliance with applicable specifications. In the event that a gasoline does not comply, CITGO instructs the gasoline distributor to discontinue distribution of the fuel and take corrective action.

Gasoline containing ethanol in concentrations up to 10 percent has been determined by auto manufacturers to be a satisfactory fuel for most late model vehicles. CITGO recommends, however, that you consult your owner’s manual before using ethanol-blended fuel to ensure that your equipment is compatible with this type of fuel. Furthermore, vehicles operating on gasoline containing ethanol may experience a decrease in fuel economy due to the lower energy content of ethanol.

CITGO is a recognized leader for our efforts in ensuring the quality of ethanol used for blending with gasoline. CITGO earned that role through its continued focus on quality and, consequently, successfully led ASTM International to develop a new ethanol specification limit that ultimately provides additional protection for consumers. Subsequently, CITGO received an award from ASTM International for successfully moving this issue to completion. In addition, General Motors recognized CITGO for our commitment to quality fuels and the motoring public. That doesn’t happen every day! It is a reflection of our commitment to you.

The Antiknock Index, commonly referred to as Octane, is a measure of a gasoline’s ability to resist preignition, or engine knock. The Antiknock Index posted at the retail pump, such as 87 Octane, is the result of a formula which most closely depicts the average resistivity of the gasoline to engine knock. This average is displayed on the gasoline pump with a sticker showing (R+M)/2 Method.

The Research Octane Number, or R in the equation, is a measure of the gasoline’s ability to resist knock at low speed under relatively mild operating conditions, such as city type driving. The Motor Octane Number, or M in the equation, is a measure of the gasoline’s ability to resist knock at high speeds and under severe operating conditions, such as towing a boat or climbing steep hills. The average of these two numbers defines how well the gasoline will resist engine knock under most conditions.

Engine knock is a sharp metallic noise, sometimes referred to as engine clatter or pinging, caused by the pre-ignition of fuel as it’s compressed in the cylinder, milliseconds before the normal spark plug firing. This condition typically occurs during acceleration, such as merging into highway traffic, or under heavy load conditions, such as pulling a boat or travel trailer. Under knock conditions, a vehicle will experience a reduction in power output as well as reduced fuel economy.

Several factors can contribute to, or result in, engine knock. These factors include outdoor temperature extremes, altitude, humidity, operating under heavy engine loads, time elapsed between routine tune-ups, vehicle age, and manufacturing and engineering tolerances. The most common cause of engine knock is improper tuning of the engine, where the engine timing has deviated from the manufacturer’s design specifications. This problem is easily resolved through proper routine maintenance and tune-ups.

As a vehicle’s engine ages, the octane required to prevent knock may increase. This condition is referred to as Octane Requirement Increase, or ORI, and is the result of normal engine wear. In instances where you experience occasional or moderate knocking, your first line of defense is to try a higher octane gasoline to accommodate this Octane Requirement Increase of your engine. Severe knocking, which cannot be remedied by using a higher octane grade of gasoline, demands your authorized mechanic’s attention.

Un-additized gasoline can leave harmful deposits in today’s fuel systems, which are technically advanced and highly sensitive to such deposits. Over time, as these deposits accumulate, a vehicle can develop drivability problems such as hesitation, loss of power, poor acceleration, rough idle or even stalling. CITGO’s gasoline detergent additive is formulated to help maintain your car’s engine at peak performance by preventing deposits from forming in critical areas.

Yes. The benefits of our additive is provided to all of our customers, regardless of the octane grade you choose.

Reformulated gasoline (RFG) is gasoline blended to burn more cleanly than conventional gasoline and to reduce smog-forming and toxic pollutants in the air we breathe. The RFG program was mandated by Congress in the 1990 Clean Air Act amendments. The first phase of the RFG program began in 1995 and the second (current) phase began in 2000.

RFG is required in cities with high smog levels and is optional elsewhere. RFG is currently used in 17 states and the District of Columbia. About 30 percent of gasoline sold in the U.S. is reformulated.

The air quality benefits RFG has achieved represent a significant part of the country's smog reduction strategy. The RFG program, combined with other industrial and transportation controls aimed at smog reduction, is contributing to the long-term downward trend in U.S. smog levels. About 75 million people breathe cleaner air because of RFG.

Yes. In fact, all automobile manufacturers have approved Reformulated Gasoline for use in their vehicles.

Your gas mileage is more affected by driving habits and vehicle maintenance than from the use of RFG. You can expect similar fuel economies from both RFG and conventional gasoline grades blended with similar amounts of ethanol.

Your first reference should be the vehicle Owner’s Manual. Each automobile manufacturer includes, in the Owner’s Manual, the recommended minimum octane for normal operation of the vehicle. As a general rule of thumb, however, use the octane grade which prevents your engine from knocking or pinging. CITGO provides three different octane grades of gasoline, complete with CITGO’s proprietary high performance detergent additive, to satisfy the needs of a wide range of vehicles and operating conditions.

We are committed to protecting your privacy and we don’t sell your personal information to anyone. Our refined Privacy Policy addresses collection and use of personal information. Like most websites, this one uses cookies for functional and analytical purposes. To learn more, please read our updated Privacy Policy. Click “OK” to acknowledge the notice of the updated Privacy.