Oil prices shot up on July 13. WTI crude—the main US benchmark—rose 3.82% to $74.14 a barrel, while Brent crude, used globally, climbed 3.88% to $78.96, according to WSJ's live markets coverage. The reason: President Trump reimposed a naval blockade on the Strait of Hormuz, a narrow waterway through which roughly one-fifth of the world's oil passes every day.

This blockade reversal matters because it undid six weeks of oil market optimism. In mid-June, the blockade had been lifted, and traders started betting that oil supplies would flow more freely. Prices fell. But this week, the blockade snapped back into place, and prices jumped right back up.

Here is what happened week by week. On June 19, seven Iranian oil tankers left port after the blockade lifted, signaling that supplies were moving again. By June 22, roughly 6 million barrels of Iranian crude had passed through Hormuz, with reports of over 30 million barrels heading to Asia. By July 1, the flow had grown to over 10 million barrels a day—the highest level in weeks. At that point, Brent crude fell below $72, the lowest price since before the conflict with Iran started. The market was convinced the supply problem had been solved.

Then everything reversed. On July 7, Washington revoked a permit that had allowed Iranian oil to be shipped. Oil jumped 3%. Two days later, Trump announced the blockade was back on—plus a 20% tax on any cargo passing through the Strait. Fresh military strikes against Iran followed. By July 13, all the June gains had evaporated.

The 20% tax is worth understanding. It is not a complete shutdown. Instead, it is a cost added to every shipment. Think of it like a toll: ships can still pass, but they pay 20% more. The market needs to figure out if this tax will actually be enforced or if it is mainly a negotiating tactic. That answer changes how permanent the current price jump is.

One more layer of uncertainty: the US and Iran are now disputing whether the Strait is even open. Markets hate ambiguity about chokepoints—they price uncertainty almost as aggressively as they price a real closure. That fog itself is keeping prices elevated.

For anyone tracking oil markets or energy stocks, the headline is simple: one policy change wiped out an entire month-and-a-half of price movement. The practical lesson for people watching closely is that positioning built on a single week's news tends to get overrun by the next week's headline.