WESTWOOD — The state’s average gas price rose 3 cents this week and is 18 cents higher than a month ago, according to AAA Northeast.

The average price for self-serve unleaded in Massachusetts is $2.39 per gallon, compared with $2.21 last month. This week’s price is 15 cents cheaper than at this time last year and 3 cents below the national average.

The average national gas price rose 2 cents from last week, to $2.42 per gallon. It is 17 cents higher than a month ago and 5 cents cheaper than at this time last year.