Gas prices are rising.

U.S. gas prices rose 3.9% in August from the prior month, accounting for more than a third of the monthly all items increase, according to the Labor Department. Fuel oil jumped 10.1%.

Prices have continued climbing in the early days of September. Escalating attacks on shipping in the Middle East have pushed oil prices to settle above $100 a barrel and reach their highest levels since May. The national average price for a gallon of regular gas rose to $4.27 on Thursday, up 13 cents from the prior week, according to AAA.