Man filling his car's gas tank | Tom Merton/OJO Images/Getty Images

Dear Driving for Dollars,

I was watching a news report about the recent jump in gas prices, and the commentator said that it is at least partially due to the new “summer blend” of gasoline. Why are there different blends of gasoline, and why in the world does it cause gas prices to go up?

— Jedrek

Dear Jedrek,

It’s easy to think that you are being taken advantage of at the gas pump when you see gas prices suddenly spike, but there is a very real reason for a sudden increase when gas pumps switch out their gasoline blends.

The 2 blends of gasoline — so-called winter and summer blends — help cars run better at different ambient temperatures. The basic difference is in something called Reid vapor pressure, or RVP. Winter blend has a higher RVP, so the fuel can evaporate in the engine properly at colder temperatures. If it weren’t used, cars would be harder to start and would run rough. Summer blend has a lower RVP to prevent excessive evaporation in hot temperatures. It also reduces the environmental pollutants that come out of your tailpipe and prevents issues such as vapor lock, a condition that can occur on very hot days (when the liquid gasoline turns to vapor while in the fuel system, effectively shutting down the engine).

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So what’s the reason for the price increase? Well, it’s twofold. First, refineries must temporarily cease production in order to prepare their equipment to produce the new blend. Since they are already shutting down, many refineries stay closed for a longer period to perform regular maintenance as well. This results in a temporary shortage of production, which causes prices to rise. In addition, summer-blend gas is more expensive to produce, and that cost is passed on to consumers. Once the refineries are all up and running, gas prices drop, but not back to the level immediately prior to the switch.

While you will pay a bit more for summer-blend than winter-blend gas, your overall costs will probably even out. The Environmental Protection Agency says summer blend contains 1.7% more energy than winter blend, so your fuel economy will be slightly improved.

Want to get even better gas mileage? Try these 4 ways to improve your car’s fuel economy.

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