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Why is gas cheaper during the winter?

The seasonal changes in gas prices aren't just due to supply and demand. The gas you're getting out of that pump changes, too.

LOUISVILLE, Ky. — Have you ever noticed that trips to the gas station feel a little less painful in the winter months? It’s a yearly ritual: gas prices go up during summer, and then fall when winter and cold weather come around.

Supply and demand are the often the explanations offered for this phenomenon, and they’re both absolutely at play here. More people are hitting the roads for summer fun, which increases the demand for gas, which in turn raises prices.

However, there’s actually another yearly pattern at work with this price cycle, and it has to do with the typical temperatures during the winter and summer. Turns out, you’re actually buying an entirely different blend of gas in the winter than you are in the summer.

“Refineries… shut down for maintenance and they change out their summer and winter blends,” said Lynda Lambert, spokesperson for AAA East Central. “They change to summer [blend] typically in the spring, maybe around April, and then they switch black to winter-blend starting in September.”

The fuel inside your car has to be able to evaporate -- that’s how your engine works. We measure the ability for fuel to evaporate with its “Reid Vapor Pressure” (RVP). The higher the RVP, the easier the fuel evaporates. 

In the winter when temperatures are colder, oil refineries distribute a blend of gas specifically made to have a higher RVP. This lets the fuel still evaporate on cold days.

“You know, you get in your car in the morning and the engine’s cold—and sometimes it turns over a couple times without starting—that higher RVP allows the engine to work even in the cold temperatures,” Lambert said. “If that RVP gets too low, then your car might not start, and if it does it might run sluggishly.”

The opposite is true in the summer. Summer-blend gas is made to have a lower RVP, preventing excessive evaporation and reducing emissions during warmer months of the year. Thing is, the blend is more expensive to make. That extra cost gets passed on to you, the consumer.

Before you get too happy about the cheaper gas prices coming at us for the winter, though, consider this: the EPA says that the lower-cost winter gas also contains slightly less energy than summer gas, so your fuel efficiency is probably going to go down a bit over the next few months.

You win some, you lose some.

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