Detroit-area gasoline will become the most efficient in Michigan on June 1, but it will come with a cost.

The Michigan Department of Agriculture and Rural Development says ozone monitoring will return to eight counties (Lenawee, Livingston, Macomb, Monroe, Oakland, St. Clair, Washtenaw, and Wayne) in southeast Michigan on June 1. The change is part of an EPA requirement introduced in 1996 to lower smog levels. It will last until Sept. 15.

The eight counties may only sell gas that does not exceed 7.0 pounds per square inch vapor pressure. In summer, the point at which gasoline turns into a gas is lower due to atmospheric pressure changes. The summer gas increases fuel efficiency. It can also increase cost.

The EPA requires all summer gas to be between 9.0 PSI and 7.8 PSI. Southeast Michigan's special requirements are part of the Clean Air Act.

How much more efficient is summer gas?

AAA says summer-blend gasoline is 1.7 percent more efficient than winter gas.

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