BOSTON — The average cost of a gallon of gasoline in Massachusetts has crept up a penny.

AAA Northeast reported Monday that self-serve, regular inched up to an average of $2.70 per gallon in the past week.

The Massachusetts price is 9 cents lower than the national average for the same grade and 13 cents lower than the per-gallon average in the state a year ago.

An organization spokeswoman says more expensive crude oil prices, robust demand, and decreasing supply all contributed to the higher costs. Hurricane Barry appears to have had little impact on prices.

AAA found gas selling for as low as $2.53 per gallon to as high as $3.05.