Why Is Gas More Expensive in the Summer Than in the Winter?

By: Jacob Silverman  | 
For the first time ever, largely due to soaring inflation and the devastating Russian invasion of Ukraine, among other causes, gas prices in California surpassed $6 per gallon, as seen here in Petaluma, May 18, 2022. Justin Sullivan/Getty Images

Unfortunately for drivers, gas prices often go up during the summer, starting around Memorial Day.

In May 2022, U.S. consumers are paying an average of $1.50 per gallon more than they were at the same time in 2021, according to AAA. The reasons are many and varied, but two causes are soaring inflation and the fact that many countries, including the U.S., have cut off oil imports from Russia, one of the world's top oil producers, due to the war in Ukraine. This volatility has shaken up the crude oil markets and continues to push prices higher.


But fuel prices typically increase every summer, and some of the reasons are fairly logical. More people traveling, especially on family vacations and road trips, increases demand. Also, in the spring months, energy companies conduct maintenance on their refineries, shutting them down and limiting capacity until late May.

Because of these disruptions, oil supplies can become stretched. In addition, natural disasters, like hurricanes, can increase prices by disrupting transport routes and damaging refineries and other infrastructure.

But did you know that the gasoline sold during the summer is actually different — and more expensive to produce — than that sold in the winter? In this article, we'll take a look at why summer fuel prices are higher, focusing on the annual shift from winter-grade fuel to summer-grade fuel.

Twice every year in the United States, the fuel supply changes. It's known as the seasonal gasoline transition. This change is the biggest reason for the price hike in summer gasoline. Depending on the time of year, gas stations switch between providing summer-grade fuel and winter-grade fuel.

The switch started in 1995 as part of the Reformulated Gasoline Program (RFG), which was established through the 1990 Clean Air Act Amendments. The Environmental Protection Agency (EPA) started the RFG program in order to reduce pollution and smog during the summer ozone season, which occurs from June 1 to Sept. 15 [source: EPA].

In order to reduce pollution, summer-blend fuels use different oxygenates, or fuel additives. These blends, the EPA says, burn cleaner and also help compensate for a limited oil supply. This practice of using seasonal blends also encourages the development of alternative fuels. (Remember that gasoline isn't just made up of processed crude oil; it's a blend of refined crude oil and different compounds and additives.)

So what's the difference between summer-grade fuel and winter-grade fuel? Summer-grade fuel burns cleaner than winter-grade fuel. This just means that it produces less smog and releases less toxic air pollutants, which we'll talk about later. The actual difference in cost of production varies and it can add between 5 and 15 cents per gallon to the cost of your fill-up, depending on the U.S. region [source: Gas Buddy]. No matter the difference in production costs, the increase at the pump is even greater, owing to the summer driving season, dips in supply, maintenance costs and companies' converting to production of summer blends.

On the next page, we'll take a look at why summer-grade fuels are more environmentally friendly and when exactly the shift between summer and winter fuels occurs.

Summer-grade Versus Winter-grade Fuel

Colonial Pipeline's Dorsey Junction Station
In an aerial view, fuel holding tanks are seen at Colonial Pipeline's Dorsey Junction Station on May 13, 2021 in Woodbine, Maryland. The Colonial Pipeline returned to operations following a cyberattack that disrupted gas supply for the Eastern U.S. for days. The EPA waived the summer fuel requirement during that time. Drew Angerer/Getty Images

During the summer, pollution is a frequent concern due to increased levels of smog and ozone, which can harm the lungs. Summer heat boosts the formation of ozone, while the appearance of an inversion layer — an immobile layer of air — can trap pollutants in the lower atmosphere [source: EPA].

Summer-grade fuel has a different Reid vapor pressure (RVP) than winter-grade fuel, which contributes to its being (marginally) more eco-friendly. RVP is the vapor pressure of gasoline measured at 100 degrees Fahrenheit (38 Celsius). Fuels with higher RVP evaporate more easily than those with lower RVP. A particular fuel blend's RVP is based on the combined RVP of the ingredients that make up the blend. Regulators worry about this evaporation because it contributes to ozone formation.


Gasoline must have an RVP below 14.7 psi (pounds per square inch), which is normal atmospheric pressure; if a fuel's RVP were greater than 14.7 psi, excess pressure would build up in the gas tank, and the fuel could boil and evaporate. Depending on the state and month, gasoline RVP may not exceed 9.0 psi or 7.8 psi for summer-grade fuel. Some local regulations call for stricter standards [source: EPA]. Because of these varying RVP standards, more than 14 different types of boutique fuel blends are sold throughout the U.S. during the summer [source: Gas Buddy].

Because RVP standards are higher during the winter, winter-grade fuel uses more butane, with its high RVP of 52 psi, as an additive. (Winter-grade gas has about 10 percent butane in its blend). Butane is inexpensive and plentiful, contributing to lower prices. Summer-grade fuel might still use butane, but in lower quantities — around 2 percent of a blend [source: The Oil Drum].

We know that gas prices go up during the summer, generally around Memorial Day, but when do companies start producing these different summer fuels? The EPA defines April to June as the "transition season" for fuel production. Refineries switch over to summer-blend production in March and April. Gas stations have by June 1 to switch to selling summer-grade gas, while terminals and other facilities "upstream" from pumping stations have to switch by May 1 [source: EPA]. Following the summer driving season, companies switch back to winter blends beginning in September, with the first winter increase in RVP allowance occurring on Sep. 15.

In a 2021 report, the EPA said that "roughly 75 million Americans breathe cleaner air today due to [the seasonal fuel] program." Still, the increased price, combined with the use of controversial additives like ethanol (which is less energy efficient than gasoline and produces more smog) and methyl tertiary butyl ether (MTBE), means that the program may still have its detractors.

In times of crisis or natural disasters, the EPA may waive the summer fuel mandates. On April 29, 2022, the EPA issued an emergency waiver for a higher-ethanol gasoline blend, allowing summertime sales of the fuel in an attempt to help lower gasoline prices at the pump, which have risen sharply largely due to inflation in the U.S. as well as the market shock caused by the Russian invasion of Ukraine, among other factors.

Two other situations that prompted the EPA to waive summer fuel mandates were the 2021 ransomware attack that caused the Colonial Pipeline (which supplies gas to states all along the East coast) to shut down and the COVID-19 pandemic in 2020. In the former case, the waiver was to keep fuel prices from getting too high and in the latter, the dropoff in gasoline demand meant that more time was needed to transition from winter to summer fuel, as gas storage is limited.

Originally Published: Jun 6, 2008

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More Great Links

  • Bailey, Ronald. "Gasoline Prices: Conspiracy or Plot?" Reason Magazine. March 23, 2007. http://www.reason.com/news/show/119300.html
  • Environmental Protection Agency. "Guide to Federal and State Summer RVP Standards for Conventional Gas Only." April 15, 2008. https://nepis.epa.gov/Exe/ZyNET.exe/P1006OTY.txt?ZyActionD=ZyDocument&Client=EPA&Index=2006%20Thru%202010&Docs=&Query=&Time=&EndTime=&SearchMethod=1&TocRestrict=n&Toc=&TocEntry=&QField=&QFieldYear=&QFieldMonth=&QFieldDay=&UseQField=&IntQFieldOp=0&ExtQFieldOp=0&XmlQuery=&File=D%3A%5CZYFILES%5CINDEX%20DATA%5C06THRU10%5CTXT%5C00000016%5CP1006OTY.txt&User=ANONYMOUS&Password=anonymous&SortMethod=h%7C-&MaximumDocuments=1&FuzzyDegree=0&ImageQuality=r75g8/r75g8/x150y150g16/i425&Display=hpfr&DefSeekPage=x&SearchBack=ZyActionL&Back=ZyActionS&BackDesc=Results%20page&MaximumPages=1&ZyEntry=4
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