Gas prices above $2.60
The average cost of a gallon of gas rose for the 40th straight day and is up more than 27% during that time.
NEW YORK (CNNMoney.com) -- Gas prices continue to surge nationwide, and are now up more than 27% in the past seven and a half weeks.
The average cost of a gallon of regular gasoline rose slightly Sunday to $2.613, from $2.606 according to motorist group AAA. This is the fortieth consecutive daily increase in the price of gas. In just the past week, prices have increased more than 4%.
Prices were highest in the state of Michigan, at $2.933 a gallon, AAA reported. They were cheapest in South Carolina, at an average of $2.394 a gallon.
Gas prices have been steadily rising since early December, when the national average was around $1.60 a gallon. But despite the recent rise, gas prices are still well below year-ago levels of $3.988 a gallon and last year's all-time high of $4.114 a gallon.
But some are concerned that prices will continue to rise. Part of that has to do with the usual increase in demand for gas during the summer months.
In addition, rising hopes of a U.S. economic rebound have helped push oil prices higher as the dollar has weakened against other currencies. A weaker greenback tends to push up the price of oil since oil is traded in dollars around the world.
Oil prices briefly traded at a 6-month high of above $70 a barrel Friday, before edging lower. Crude prices closed at $68.44 a barrel. 
