Gas is now under $4 a gallon on average in these Massachusetts counties

SPRINGFIELD - Gas for under $4 a gallon is becoming an increasingly common sight in Massachusetts.

As of Thursday, AAA's gas prices map shows four counties in Massachusetts with sub-$4 prices: Bristol ($3.99), Hampshire ($3.98), Hamden ($3.91) and Franklin ($3.89).

Statewide, the average cost of a gallon of gas is $4.12. Gas is still averaging more than $5 a gallon on Martha's Vineyard and Nantucket. 

The national average is $3.87 per gallon. 

Click here for the latest county-by-county gas prices in Massachusetts.