April 11 (UPI) -- A steady rise in crude oil prices and maintenance at the nation's refineries means steady pain at the pump for U.S. motorists, motor club AAA reports.
AAA lists a national average price for a gallon of regular unleaded gasoline at $2.39, up slightly from Monday for nearly a two-week streak of gains. By the motor club's estimates, the national average for the price of gas is up more than 4 percent, or about 10 cents per gallon, from one month ago.
"Pump prices in 48 states and Washington D.C. have moved higher over the last week, led by the switch over to more expensive summer-blend gasoline and increased driving demand," AAA explained in a weekly retail market report.
The summer-blend of gasoline is more expensive to produce because more steps are needed to prevent evaporation during warmer months. The end of winter across much of the Lower 48 also means drivers are taking to the road to break cabin fever and both factors can weigh on demand.
Adding to the situation is a steady gain in crude oil prices. Markets were moving higher in late March amid signs of a crimp in supplies and a U.S. decision last week to launch airstrikes on targets in Syria pulled crude oil prices higher because of the regional tensions that followed.
By region, the West Coast is the most expensive market in the country and AAA said that won't change anytime soon. California gas prices are hovering near $3 per gallon and could break through the psychological price-point given refinery maintenance at a PBF Energy facility in California and maintenance at a BP plant in Washington.
The Great Lakes market remains the most volatile in the country and Michigan held the distinction of the state with the largest increase in gas prices, up 12 cents from last week for a state average of $2.55 per gallon. As an indication of regional volatility, state prices across the border in Ohio are 7 percent lower.
According to AAA, there are two refineries in the area that are operating at reduced capacity because of maintenance work.
The U.S. government estimates the national retail price for the year will average $2.40 per gallon.