The U.S. Energy Department's Energy Information Administration said Midwest gasoline prices have been on the rise since mid April.
"Higher gasoline prices in the Midwest largely reflect supply constraints stemming from decreased refinery runs and lower-than-normal gasoline inventories," the EIA said. "Refinery utilization in the Midwest has fallen steadily since the start of 2013 and is now about 83 percent of capacity, below the U.S. average of 87 percent."
The EIA said consumers in Minnesota were hardest hit, with gasoline prices as of May 20 at $4.29, more than 60 cents higher than the national average for a gallon of regular unleaded.
Gasoline prices in general have increased for the week of May 20 as U.S. consumers prepare to travel for the Memorial Day holiday. Motor group AAA reports the average national price for Friday was $3.65 per gallon, 4 cents higher than last week.
The EIA reports that U.S. consumers should pay about $3.53 for a gallon of regular unleaded gasoline this summer, down from last year's average.
Further north, the Canadian National Energy Board reports that consumers should be about the same for gasoline as they did last year, with a summer average between $4.38 per gallon and $4.68 per gallon.