The Feds Are Going To Let Gas Stations Sell Winter Gas In The Summer. Here’s What That Means For Your Car

If you’ve paid any attention to the news these past few weeks, or simply stopped at a gas station to fill up your tank, you’ve probably realized that gas prices are on the rise. The new conflict in Iran, as well as the ongoing war in Ukraine, means prices are probably going to stay elevated through the summer, which means you’ll likely be paying more for that summer road trip than you expected.

In an effort to curb rising prices, the Environmental Protection Agency (EPA) announced yesterday plans to issue a waiver to allow the nationwide sale of E15 gasoline—gas blended with 15% ethanol, popularly known as “winter gas”—during the first 20 days of May.

Compared to Summer-grade gasoline, winter gas is cheaper because it’s slightly less energy-dense. That also means it’s a tiny bit less efficient. And depending on what car you drive, it could do more harm than summer gas on your fuel system. Here’s what you need to know.

What’s The Difference Between Summer Gas And Winter Gas?

Back in 1989, the EPA began putting limits on the volatility of gasoline sold at gas stations nationwide. “Volatility,” in this case, doesn’t refer to my portfolio of high-risk tech and healthcare stocks I’m too ashamed to admit my lifetime gains/losses on. Instead, volatility is the point at which liquid evaporates, turning into vapor and entering the air. This is bad, as gas vapors contribute to smog, which can cause respiratory issues for people.

This law outlaws the sale of gasoline with a Reid vapor pressure (RVP) of over 9 pounds between June 1 and September 15, according to Car and Driver. In places like California, that time window is extended to between April 1 and October 31. RVP, according to the American Society for Testing and Materials, is the gasoline’s vapor pressure at 100 degrees Fahrenheit.

There are a lot of additives that fuel suppliers use to adjust RVP, but ethanol is the most significant. Basically, the more of the corn-based fuel you have in the gas, the higher the fuel’s RVP will be. And the higher the RVP, the more easily it will evaporate from your gas tank when it’s hot outside. During summer months, E10—that is, gasoline blended with 10% ethanol—is the standard, as that’s the most suppliers can add before reaching that EPA-enforced RVP limit. During the winter months, when the gasoline isn’t as susceptible to evaporating, more Ethanol is added to the mix.

Why is the percentage of ethanol higher in the winter? Well, in addition to offering a higher-volatility blend that works better in colder temperatures, it means the fuel can be cheaper. Amsoil explains it well in its blog on the subject:

Winter-blend fuel requires increased RVP. If the fuel doesn’t evaporate readily in cold temperatures, the engine will start hard and run rough when it’s cold outside.

To achieve this, refiners often blend winter gasoline with butane, a relatively inexpensive additive with a high RVP. They adjust the RVP of the final formulation to as high as 15.0 psi to help the gasoline ignite readily in the cold.

Of course, because Butane has a high RVP, it can’t be used during the summer because of the EPA’s rules. Here’s Amsoil explaining how fuel manufacturers make the switch:

Once the temperature warms up in summer, however, high-RVP gasoline can volatilize more easily, which contributes to increased emissions and air pollution.

For that reason, federal law restricts sales of gasoline with an RVP greater than 9.0 from June 1 through Sept. 15.

To comply, refiners reduce the amount of butane in the gasoline and instead use pricier additives, hence one reason gas prices generally increase in summer. The blending process also takes longer, adding to the cost.

So, now you know what those labels on the gas pump talking about ethanol blend are all about – not that it’s likely to matter much if you drive a remotely modern car.

How Does It Affect My Car?

The EPA says that cars after 2001 can safely handle gasoline with up to 15% ethanol blend, and that’s true for “flex fuel” cars, which are designed from the factory to handle up to 85-percent ethanol blends. But as Thomas wrote last year, some manufacturers don’t recommend it:

[T]here are lots of vehicles made after 2001 that aren’t designed for E15. For instance, BMWs only approves a maximum of 10 percent ethanol content in its vehicles, as does Mazda, as does Mercedes-Benz on all models not approved for E85. Volvo only approves a maximum of 10 percent ethanol content across its lineup, as does Mitsubishi.

Some other manufacturers like Nissan are more selective when it comes to E15 approval. The current Frontier, Rogue, Z, Pathfinder, and Altima can take E15, but the Sentra, Kicks, and almost all outgoing models like the previous-generation Armada aren’t rated to handle it.

The thing with ethanol is that it’s hygroscopic, which means it pulls in moisture from the air. And having water mixed in with your fuel is, of course, very bad. Anyone who’s seen those videos of vehicles attempting to ford a water crossing only to hydrolock their engines knows that. Also, ethanol, when mixed with oxygen, can form acetic acid, which is the active ingredient in vinegar. While the stuff is good for cooking and cleaning rusty car parts, it’s not so great for fuel system components.

Of course, that doesn’t mean your car will immediately fall apart if you run E15 through it. You’ve probably been doing it all winter without even knowing, along with millions of other drivers on the road. Today’s fuel systems are sealed pretty well, which means water egress isn’t a huge issue. If anything, the rubber hoses in your fuel system might degrade slightly quicker over the life of the car than if you ran E10 year-round. If you have an older car with rubber hoses that aren’t designed to handle ethanol, you might want to be a bit more cautious.

More important is the difference in energy content between winter gas and summer gas. Ethanol is about 30% less energy-dense than gasoline, which means the drop in ethanol from E15 to E10 results in summer gas being roughly 1.7% more energy-dense, according to Car and Driver. That’s enough for a small (but measurable) increase in fuel economy, all other things equal. So while winter gas might be cheaper, you might not actually be saving any money, since you’re using more fuel to drive the same distance.

Why Is The Government Doing This?

Officially, the EPA says it’s issuing a waiver to give drivers more options as the country inches closer to the Summer driving season. Here’s the relevant stuff from the announcement:

Through the waiver, EPA is fortifying the domestic gasoline supply chain and providing Americans relief at the pumps ahead of the summer driving season. Beginning on May 1, 2026, EPA’s waivers will work to prevent disruption in America’s fuel supply by keeping E15 on the market and giving Americans more fuel options.

According to the EPA, not only will drivers benefit thanks to lower prices, but corn farmers will also see a benefit thanks to the increased demand for ethanol, which is derived from corn. The announcement even threw in a quote from the Secretary of Agriculture:

Allowing the summer sale of E-15 will provide drivers more options at the pump, and deliver a bigger domestic market for American farmers,” said U.S. Secretary of Agriculture Brooke L. Rollins. “While today’s announcement is great news for farmers, year-round E-15 is essential for the farm economy, and Congress needs to find a common sense solution that provides much needed certainty to consumers and farmers.

The savings found at the pump are debatable for the energy density reasons mentioned above, but whether people actually realize that the slightly lower prices won’t actually result in any money saved is another story. As Bloomberg points out, the timing of this move to lower prices comes during a midterm election year, when voters are increasingly faced with higher costs of living. It’s a safe bet to assume this waiver is being used to counter the spike in oil and gas prices from the current conflict in Iran.

This isn’t the first time we’ve seen an admin use waivers on RVP to drive down fuel prices during an election cycle. The Biden administration did the same thing back in the spring of 2022, claiming to counter fuel price increases due to the war in Ukraine (though pandemic-induced supply chain ripples also contributed to those price jumps). These emergency waivers have been extended several times since, and they’re continuing again into the summer of 2026.

What does this mean for the environment? Well, more E15 gas in cars means more gasoline evaporating into the air when it gets hot out, which will likely result in more harmful smog. But that tracks with this current admin. Last year, it eliminated penalties for manufacturers that don’t meet corporate fuel economy targets and announced a $625 million investment into the coal industry. The push to keep winter gas flowing comes just three days after the Department of the Interior agreed to pay French company TotalEnergies $1 billion to walk away from an offshore wind power lease, directing the company to use that money towards natural gas projects instead. The government’s priorities are clear.

While this waiver is only set to last a few weeks, the EPA says it’s “ready to extend the emergency fuel waivers as long as the fuel supply circumstances warrant such action.” Seeing as how the waiver’s been extended for the last few summers past, I would count on that happening.

Top graphic image: DepositPhotos.com