U.S. gas prices up, and expected to keep rising

April 3 (UPI) -- Gas prices may continue to move higher in the United States as refineries start to shift to a summer blend, which is more expensive to make, AAA reports.

While the weather across some of the United States might not show it, it's officially spring and retail stations are getting rid of a winter-blend of gasoline to make room for a formula that's more expensive because of the additional steps necessary to stave off evaporation during the warmer months.

Motor club AAA reports a national average retail price of $2.66 for a gallon of regular unleaded for Tuesday, up 5 cents from last week, 11 cents more than two weeks ago and 33 cents more per gallon than this time last year.

Retail prices nation-wide, as reviewed by GasBuddy, show the average price for gas is the highest it's been in nearly three years. Adding to the pain is a hike in crude oil prices, which are up more than 5 percent since the beginning of March.

"Today, only 38 percent of U.S. gas stations are selling gasoline for $2.50 or less and that percentage will likely dwindle in coming weeks," AAA spokeswoman Jeanette Casselano said in a statement.

By market, drivers in the West Coast are paying the most for gasoline, with California, Nevada, Oregon and Washington all posting prices above $3 per gallon. California leads in the Lower 48 with $3.51 per gallon, only a penny less than in Hawaii.

Federal estimates show the regional rate of gas production is more than 30 percent below the rate from last year. A Phillips 66 refinery in the Los Angeles region, meanwhile, is scheduled for maintenance and that will cut supplies even further.

The Great Lakes region, meanwhile, is the most volatile, with Michigan leading the pack with a 3 percent hike in retail gas prices over the last week. That comes even as the region sits on some of the highest stockpiles of gasoline in the region. Prices there tend to be fluid because of stiff competition at the retail level.

Federal data, meanwhile, show that gasoline demand fell to its lower point for March, though it remains relatively strong for this time of year.