The average price for a gallon of regular gasoline in the United States increased 6.8 cents in the last two weeks due to a rise in crude oil prices partly driven by tensions in Iran, according to the nationwide Lundberg Survey.

According to the survey of some 2,500 gas stations in the continental United States, the national average for regular gasoline as of Aug. 24, was $3.759 per gallon, up from $3.69 on Aug. 12. It was about 21 cents below the April 6 peak price of $3.967 a gallon.

"Higher crude oil and ethanol prices remain the two biggest causes of higher gasoline prices," survey editor Trilby Lundberg said.

Chicago reported the highest average price for self-serve, regular gasoline in the two-week survey period at $4.22 a gallon, while drivers in El Paso, Texas, got off more cheaply with $3.32 a gallon, according to the survey.