Average gasoline prices fell in 47 states over the last week, with the national average dropping below $4 per gallon late Sunday night for the first time since mid-April. GasBuddy says the decline came as oil prices moved sharply lower in reaction to news of a potential deal between the United States and Iran, although it remains to be seen whether the agreement will hold. Average gasoline prices in Minnesota have decreased by 11.1 cents per gallon over the last week, averaging $3.85. The national average price of gasoline has fallen 9.3 cents per gallon in the last week, averaging $3.99. The national average price of diesel has decreased 11.7 cents compared to a week ago and stands at $5.18 per gallon.