How Gasoline is Made
The refining process separates crude oil into its various components, which can be further processed and blended to make gasoline and a variety of other products.
What is Gasoline?
Gasoline is a precise blend of components designed not only to ensure peak engine performance, but also to meet strict environmental standards. Today's gasoline must:
Allow instant engine start-up and smooth acceleration in both cold and hot weather
Run cleanly with a low gum content and detergent additives to prevent valve sticking and engine deposits
Vaporize properly for your specific climate and altitude to prevent vapor lock
Burn efficiently to minimize volatile organic compounds (VOCs) in the exhaust which can react with sunlight and contribute to air pollution
Avoid engine "knocking"
Contain minimal contaminants such as sulfur which interfere with vehicle pollution control equipment and carry an unpleasant odor
Contain required government-mandated special components, like oxygenates (alcohols or ethers)
The Refinery: Where Crude Oil Becomes Gasoline
Gasoline is manufactured in a refinery, using heat, pressure and chemical reactions to transform crude oil into hundreds of products consumers need gasoline, diesel, jet fuel, motor oil, greases and chemical feedstocks.
Refining begins by running the crude oil through a pipestill or "distillation tower," similar to a distillery. Intense heat is used to vaporize most of the oil. As the vapors rise inside the tower, different compounds cool and separate. Heavier molecules rise a short distance, while lighter ones rise farther. As the various "fractions" condense to liquid form, they accumulate on collection trays at varying heights inside the tower. This process separates crude oil into its various components based upon the weights of their molecules.
A modern day refinery uses a variety of processes and chemical catalysts to break down and then recombine molecules to maximize production of gasoline and other high-demand products, each manufactured and blended to precise specifications.
In early refineries, these different components were sold or blended into saleable products. The light liquids were used to make gasoline, the middle distillates were sold as kerosene, while the heaviest products became industrial fuels. Many gases with no commercial use were simply burned off. If a refiner wanted to make more gasoline, he had to run more crude oil and then find a way to sell the additional heavier products that came along with it.
Over the years, automobile engines, airplanes and modern industrial facilities created a demand for new cleaner, higher-performing products and lots of them.
Refineries clearly needed better ways to produce the products consumers wanted and not just ways to sell whatever products the crude oil contained. New technology was needed not only to separate crude into its components, but to actually convert some molecules into others. The first such technologies were developed during the 1920s and 1930s in Europe and the United States.
Shortly before World War II, ExxonMobil developed fluidized catalytic cracking or "cat cracking," which remains the workhorse of modern refineries. This process breaks apart or "cracks" heavier hydrocarbon molecules into lighter components, producing more and better quality gasoline from every barrel of crude oil. This technology gave Allied pilots the fuel needed for the high-performance military aircraft that helped win the war. Fortune Magazine called cat cracking "the most revolutionary chemical engineering achievement in 50 years."
And that technological revolution has continued. Today's modern refineries utilize a range of advanced technologies including hydrocracking, reforming, thermal cracking, coking, delayed coking, fluid coking, flexicoking, alkylation, hydrotreating and alkali treating. Some processes use a combination of heat and pressure to break the larger, heavier molecules into smaller, lighter ones. Others, such as alkylation, convert lighter gases into heavier, more valuable liquid fuels. Most use special catalysts that increase the yield of the most desirable products such as gasoline and lubricating oils. All are designed to take crude oil and make the products customers want as efficiently as possible.
Meeting Consumer Needs
Refineries are designed to produce the products most needed in the markets they serve. In Europe, with smaller cars, greater population density and a higher share of diesel vehicles, consumers use proportionately less gasoline than in the United States. Developing countries may have a higher need for industrial and commercial energy. As a result, a typical U.S. refinery may produce up to twice as much gasoline from each barrel of crude as a European or Asian refinery. Gasoline-intensive refineries are called "high conversion" plants because a complex set of sophisticated equipment is used to convert heavier molecules into the lighter components needed to make gasoline.
As vehicle engines have become more sophisticated, gasoline specifications have grown far more complicated. Also, as concerns over the environment have grown, the demand for cleaner-burning gasoline has increased.
Today, meeting worldwide gasoline demand is a high tech, complex and competitive business. It requires multibillion-dollar refineries and expert chemical engineers and scientists working at the leading edge of technology to use every available oil molecule to make the products customers want.
Researchers are working not only to make today's fuels better they are also developing fuels for tomorrow's vehicles. These include advanced internal combustion engines and fuel cells that convert gasoline directly into electricity.
Investment in Clean Air
More than a quarter-century of effort by industry and government has reduced new vehicle exhaust emissions by more than 95 percent in the U.S. Urban air quality in the major industrial countries continues to improve even as their economies grow. The developing countries are following suit, as their economies become better able to support newer vehicles and other environmental improvements.
Since the late 1960s, the oil industry has continuously upgraded gasoline formulations to provide the fuels required for newer and increasingly sophisticated vehicles and stricter environmental standards.
What's changed in our gasoline?
Unleaded Gasoline. Historically, lead compounds were added to gasoline to reduce "knocking" and improve engine performance. The United States began reducing lead in gasoline in the early 1970s for health reasons. Lead was phased out completely in the 1980s with the introduction of catalytic converters on automobiles, advanced emission control devices which cannot tolerate lead. Leaded gasoline has now been phased out in Europe, Japan and many other parts of the world. ExxonMobil is supporting efforts to eliminate lead from gasoline in the remaining countries.
Lower Sulfur. Low-emission vehicles are sensitive to sulfur, a compound occurring naturally in crude oil. Refiners currently remove 97-98 percent of the sulfur from gasoline in the United States and Europe.
Modern technology allows refiners to produce the products their customers need.
As engine technology continues to develop, the oil industry will need to supply the lower-sulfur fuels required. The U.S. has mandated a further 90 percent reduction in gasoline sulfur down to 30 parts per million (ppm) by 2004-2006. Europe and Japan have set a 50 ppm standard for 2005 and are considering further steps. We also anticipate requirements for lower sulfur fuels over time in the developing countries, as newer vehicles replace older ones. Sulfur standards should stay closely matched to vehicle requirements.
Vapor Pressure Reduction. Gasoline contains some light components that vaporize easily for easy engine starting and smooth warm-up. These light compounds also increase the amount of gasoline a refinery can produce.
Unfortunately, light components can also evaporate, contributing to atmospheric ozone and smog formation. Some countries are reducing gasoline vapor pressure levels (known as Reid Vapor Pressure or RVP) to help improve local air quality. Throughout the U.S. and many other countries, gasolines are blended to attain an RVP optimized for the consumer's particular climate, altitude and season.
Reformulated Gasoline (RFG). The U.S. Clean Air Act Amendments of 1990 mandated a two-stage change in gasoline composition ("reformulation") to reduce the impact of gasoline on smog formation in those areas of the country not meeting air quality standards. Beginning in 1995, Phase I required the addition of components called oxygenates (usually either MTBE or ethanol) and a reduction in emissions of unburned fuel (known as volatile organic compounds or VOCs). In 2000, Phase II mandated a reduction in emissions of nitrogen compounds (known as NOx) and a further reduction in VOCs.
The environmental benefits of reformulated gasoline could now be attained at lower cost without the use of oxygenates.
While all gasoline has the same basic components, refineries around the world must produce a variety of grades to meet specific local conditions and government regulations. The trend to "boutique fuels" raises the cost of gasoline to consumers and can lead to localized supply problems, since supplies from one area can't always be used to meet shortages elsewhere. During 2000, for example, more than a dozen different types of gasoline were required by law in the U.S.
ExxonMobil has ownership interest in 46 refineries to meet the needs of its customers around the world.
The fuel changes we have made so far have brought significant environmental improvements, but have also raised the cost of making gasoline. For the 10-year period 1989-1998, industry invested more than $44 billion in U.S. refining including more than $20 billion to meet new environmental regulations.
Reliance on good scientific evidence and rigorous "well-to-wheel" economic analysis will allow policy-makers to determine when the benefits of new fuels outweigh their costs to consumers. This approach will allow us to continue our progress toward cleaner air while still providing consumers with reliable supplies of competitively priced gasoline.