US petrol reached $4.018 per gallon nationally on 31 March, the first time above $4 since 2022, with California at $5.89 and the $1.04 monthly increase the largest single-month jump in AAA records. Pump prices had already posted their fastest monthly surge in thirty years before the Oval Office speech; crossing $4 transforms the war's economic cost from data point to lived experience for ordinary Americans.
Four dollars per gallon is not an economic threshold; it is a political one. Every prior US president who has presided over $4 petrol has seen approval ratings drop. A majority of Americans had already said the Iran war was the wrong decision before the price hit $4; the milestone will deepen that sentiment. The $1.04 monthly increase means the political cost has arrived at speed, not gradually.
Brent had surged past $112 in two separate episodes during the conflict before settling at $107.72 on the withdrawal announcement. The war had already caused a 2 million tonne US fertiliser shortfall at spring planting season, compounding upstream agricultural costs. The Philippines had declared an energy emergency on Day 26; the $4 milestone is the US domestic equivalent of that moment.
Trump has responded by abandoning Hormuz reopening as a war objective, telling the market that $4 petrol is the new floor rather than a temporary crisis. California at $5.89 represents the upper range of sustained disruption. If Iran's six-month war timeline holds, the $14-18 geopolitical risk premium embedded in Brent is substantially understated.
