DENVER (KDVR) — Colorado’s gas prices are currently among the lowest in the country, but drivers are warned: It will not last long.

As of Thursday, Colorado had the second-cheapest gas in the nation, according to AAA. The average of $3.16 per gallon for regular unleaded fuel is 51 cents below the national average.

AAA said the figure reflects lower demand as ski season winds down, but summer travel season is just ahead — and so are federal mandates for reformulated gasoline.

“Coloradans should make the most of comparatively low prices while they can,” Skyler McKinley, regional director of public affairs for AAA, said in a release. “Looking ahead to a robust summer travel season combined with the long-expected, EPA-mandated switchover to reformulated gasoline, it won’t be long until Colorado sits above the national average.”

Summer fuel blend required in the Denver area

Starting this summer, the Environmental Protection Agency will require reformulated gasoline sales in the Denver area. This is because the EPA downgraded the Front Range metro area as a “severe” violator of ozone pollution standards.

The reformulated gas evaporates less easily at higher temperatures. That matters, because fuel vapor contributes to unhealthy ground-level ozone and smog — something the EPA is trying to curb in the Denver area.

The downside: Reformulated gasoline costs more. McKinley said consumers could see the price increase by mid-May before the EPA rule goes into effect on June 1.

For an idea of what the price could look like, look to the East Coast. The region is switching to summer blend fuel and is expected to see gas prices rise by 20-50 cents a gallon, MarketWatch reported this week.

Aside from the environmental benefits, there’s another upside to reformulated gas: Drivers will get better mileage. This is because summer blend fuel contains less butane, meaning 1.7% more energy to power a vehicle, according to AAA.

Cheapest gas prices in the US

According to AAA, here are the least-expensive states for fuel right now:

Mississippi: $3.11

Colorado: $3.16

Louisiana: $3.18

Oklahoma: $3.22

Arkansas: $3.23

New Mexico: $3.26

Tennessee: $3.26

Kansas: $3.26

Alabama: $3.27

South Carolina: $3.27

Most expensive gas prices in the US

And here’s which states are listed among the most expensive:

California: $5.45

Hawaii: $4.78

Washington: $4.67

Nevada: $4.63

Oregon: $4.44

Alaska: $4.37

Arizona: $4.13

Utah: $3.96

Illinois: $3.96

Idaho: $3.93

How long is summer fuel required in Denver?

The EPA requires reformulated gasoline sales from June 1 to September 15.

Counties in the nonattainment area include Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, Jefferson and parts of Larimer and Weld.