The national price of regular unleaded crept higher to $2.87 per gallon, a one-cent increase that may lead to even higher prices in the weeks to come as summer gasoline demand remains strong, according to AAA.

The current price level is six cents higher than a month ago and 61 cents higher than a year ago.

Pump prices in nearly 30 states moved higher – some by as much as eight cents – for the week, while 12 prices in 12 states fell and prices in another 12 remained stable.

"Demand for gasoline this summer remains very strong week-over-week, driving gas prices higher alongside rising crude prices," said Jeanette Casselano, AAA spokesperson. "Today motorists are seeing gas for $2.76 or more at 56% of gas stations across the country."

The highest weekly price increases came in Delaware (eight cents), Ohio (six cents), Indiana (five cents), and Maryland. Michigan saw the largest decline of seven cents.

States with the least-expensive gas include South Carolina ($2.53), Alabama ($2.53), Mississippi ($2.55), Louisiana ($2.58), and Arkansas ($2.60).

Meanwhile, the average price of a gallon of diesel increased seven-tenths of a cent to $3.243, which is 76.2 cents higher than a year ago, according to the U.S. Energy Information Administration.

Related: Controlling Fuel Costs as Gas Prices Rise