Summer gas prices peaked in May and industry experts expect the downward trend to continue for the rest of the year.

Since May, gas prices around the country have fallen about seven cents to $2.89 for U.S. regular-grade retail gasoline, according to the latest release from the U.S. Energy Information Administration.

The price of gas in Louisville mirrored the U.S. average for the month of June, according to GasBuddy.com.

Gasoline is almost always more expensive in the summer, said industry economist Sean Hill.  That’s because demand is higher.

“Gasoline consumption, it peaks in the summer months. No surprise that’s when a lot the country takes vacation time,” Hill said. “The weather is nicer in general and people are just driving more.”

Summer-grade gasoline is also more expensive to manufacture. That’s because it’s designed to improve air quality.

“Basically less of it is going to evaporate in your gas tank as you sit on the highway,” Hill said.

Gasoline evaporates into volatile organic compounds (VOCs) that mix with nitrogen oxides and form ozone — the main ingredient in smog.

Ozone is most likely to reach unhealthy levels on hot, sunny days, and Louisville has traditionally struggled with the pollution due in part to the city’s location in a valley.

Ryan Van Velzer is WFPL's Energy and Environment Reporter.