Every spring you see gas prices rise across the U.S. You might ask yourself why? AAA Regional General Manager for the Mohawk Valley, Ed Welsh, says it’s simply because of the way the gas is made.

"It happens mainly because the refineries change over the type of gas they actually manufacture,” said Welsh.

The process is simple. Oil companies drill for the oil, refine it in plants, and then distribute blends to gas stations. In the northeast alone there are two blends, winter and summer, each having their own vapor pressure.

According to AAA, each blend is used for a scientific reason. The reasoning involves the temperature change and how easy the gas is evaporated under cold temperatures.

For example, as the temperatures decrease in the air, fuel pressure increases to create a clean burn. Studies show if this process is not done, car engines will run rough.  

Yajaria Hernandez, an Uber driver, says she notices a change in her gas mileage in the winter months.

"Well, I see the difference in the winter time,” she said. “I spend more on gas because of the weather."

According to the U.S. Environmental Protection Agency (EPA), the summer-blend gas contains 1.7 percent more energy than winter-blend gas, which is one reason why gas mileage is slightly better during the summer.