BOSTON (AP) — Gas prices in Massachusetts are down by four cents this week.

AAA Northeast found in its weekly survey released Monday that the price of self-serve, regular is averaging $2.51 per gallon. That price is four cents above the national average— $2.47 —and 38 cents higher than the average price in the state a year ago at this time.

AAA also found a 50-cents range in prices for self-serve, regular, from a low of $2.29 to a high of $2.79 per gallon.