The national average price of a gallon of gasoline dropped below $4 on Thursday, according to AAA.
Pump prices have been falling for four straight weeks. Since May 21, the national average has dropped from $4.56, the recent peak. On Thursday, AAA said gas had declined to $3.99 and nine-tenths.
The peace deal between the U.S. and Iran has sent oil prices plunging, dragging down gasoline prices. Brent crude, the global oil price benchmark, fell to around $78.45 a barrel on Thursday morning, down from around $112 in the third week in May. West Texas Intermediate, the U.S. benchmark, fell to $75.29, down from $108.
Diesel prices are also falling. A month ago, the national average for a gallon of diesel was $5.63. As of Thursday, it had fallen to around $5.13.
California has the highest state average price in the U.S., at $5.64 a gallon. The lowest state average is in Indiana, where a gallon of gas costs just under $3.40.