President Donald Trump has instructed the US Department of Justice to open an immediate investigation into major oil companies, accusing them of failing to pass on steep declines in crude oil prices to consumers at the pump. In a post on his Truth Social platform, Trump said the firms were “gouging” customers, adding that petrol prices should be falling “a lot faster than what I’m seeing.” The White House and the justice department did not respond to requests for comment outside regular business hours, and no companies were named in the post.

The intervention follows dramatic swings in global energy markets triggered by the US-Israeli military strikes on Iran on 28 February. Tehran’s effective closure of the Strait of Hormuz, a chokepoint for roughly one-fifth of global oil supply, sent Brent crude to nearly $120 per barrel in May. Since Washington and Tehran reached an interim peace memorandum and the strait began reopening, crude has tumbled: Brent now trades around $77 and West Texas Intermediate below $73. Yet average US pump prices, while down 14 per cent from a May peak of $4.56 per gallon to about $3.90, remain well above the $2.76 recorded in January before the conflict. Over the same period, crude prices have fallen by 23 per cent, and from their March peak they have dropped roughly 40 per cent.

Viewed from Washington, the president’s order comes as consumer frustration over fuel costs threatens Republican prospects in November’s midterm elections, where the party is defending narrow congressional majorities. Iranian state media, by contrast, framed Trump’s anger as a consequence of what it termed his own “illegal aggression” against Iran, noting that price spikes had already drawn criticism from US senators and officials. Analysts in London and Asian trading hubs caution that retail fuel prices typically lag crude movements by several weeks or even months, owing to refining, inventory and distribution cycles. The head of Japanese shipping operator Mitsui O.S.K. Lines has estimated that fully normalising tanker traffic through Hormuz could take up to a month, further slowing the transmission of lower crude costs to forecourts.

The justice department has yet to outline the scope or timeline of any probe. With peace talks between US and Iranian negotiators continuing in Switzerland, crude markets remain sensitive to diplomatic signals, and further gradual easing of pump prices is expected, though a rapid return to pre-conflict levels is seen as unlikely by industry forecasters.