Gasoline prices in the U.S. fell below $4 a gallon on Thursday for the first time in nearly three months, after surging as global oil prices shot up amid the war in Iran. 

The national average for a gallon of gas dropped to $3.99, the lowest level since March 30, according to AAA. Gas prices are still up by more than a dollar since the war started, but have receded in recent weeks as crude prices dropped in expectation of a preliminary deal between the U.S. and Iran to end the conflict. 

A memorandum of understanding between the countries to end the war reopens the Strait of Hormuz, a vital waterway through which one-fifth of the world's oil supply normally flows. The passage has been virtually closed since the war began on Feb. 28, driving up oil and gas prices. 

More ships began moving through the strait after Mr. Trump formally signed the agreement on Wednesday, with at least 10 commercial vessels traversing the waterway.

Brent crude, the international standard, sank 1.4% on Thursday to $78.46 a barrel, while West Texas Intermediate, the U.S. benchmark, was down 2.2% to $75.10 a barrel.

Will gas prices keep dropping?

Patrick De Haan, a petroleum expert at GasBuddy, said in a report this week that the national average for gas could continue to decline, "provided there isn't a drastic reversal and the U.S. and Iran continue moving in a positive direction."

He estimates that the cost of regular gas could fall below $3 a gallon by the end of this year or in early 2027, depending on how the situation in the Middle East unfolds. 

"One note that could improve the timeline is that Iran is allowed to sell oil on markets again, which could speed up the recovery for global oil inventories," he told CBS News in an email.