Oil prices surged after the U.S. and Israel launched massive attacks against Iran, raising fears of a wider regional war and prolonged disruption to energy flows through the Strait of Hormuz, the world’s most critical oil chokepoint.

In afternoon trading in Europe, Brent crude rose 7.8% to $78.57 a barrel after climbing above $82 in the early hours. The U.S. benchmark, West Texas Intermediate, gained 6% to $70.57 a barrel, having surged to $74 earlier. European natural gas prices also spiked, with the most-active TTF front-month contract jumping 24.6% to 39.81 euros a megawatt-hour.

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American and Israeli forces targeted Iran’s leadership and military in a barrage of strikes over the weekend, after a third round of nuclear talks between Washington and Tehran ended without a deal. In response, Iran launched retaliatory attacks against U.S. and Israeli interests, including military and civilian targets in the United Arab Emirates and other neighboring countries.

“U.S. and Israeli attacks on Iran—met with retaliatory strikes by the Islamic Revolutionary Guard Corps—represent one of the most serious threats to Middle East energy supplies in many years,” said Ole Hansen, head of commodity strategy at Saxo Bank.

The biggest risks to global oil markets stem from potential strikes on key oil infrastructure in the region or a prolonged disruption to shipping through the Strait of Hormuz, the narrow waterway at the mouth of the Persian Gulf that handles roughly a fifth of the world’s oil shipments.

Around 20 million barrels of crude oil and refined products pass through the strait each day, meaning even limited shipping delays could have significant implications for supply chains.

Tanker traffic has largely come to a standstill, with many vessels turning back, rerouting or idling nearby after Iran’s Islamic Revolutionary Guard Corps warned ships to avoid the passage. Confidence deteriorated further following reports of multiple vessel attacks and a rapid repricing of war-risk insurance, as underwriters signaled higher premiums and issued cancellation notices, market watchers said.

Shipping advisories also cited increased electronic interference affecting navigation and tracking systems across the wider area, heightening the risk of accidents. “The weekend underlined how quickly an ‘open’ strait can become functionally constrained when security alerts, insurance costs and interference converge,” analysts at Kpler said.

While Saudi Arabia and the UAE have pipelines bypassing the Strait of Hormuz, they can’t fully compensate for the waterway’s capacity in the event of a full closure. Goldman Sachs noted estimates vary, but according to the International Energy Agency, about 4.2 million barrels a day of oil flowing through the Strait could be redirected using existing spare pipeline capacities—implying roughly 16 million barrels a day could be at risk.

“The most immediate and tangible development affecting oil markets is the effective halt of traffic through the Strait of Hormuz,” said Jorge Leon, head of geopolitical analysis at Rystad Energy. “This appears to be driven by heightened tensions and precautionary decisions by ship operators and insurers rather than a confirmed physical blockade by Iran.”

More prolonged disruptions could choke oil exports, potentially driving crude prices to $100 a barrel—a politically sensitive risk for President Trump ahead of November’s midterms. Beyond oil, any disruption would also threaten liquefied natural gas shipments, as around 20% of global liquefied-natural-gas trade passes through the strait, primarily from Qatar, the world’s second-largest LNG exporter.

“Oil upside may be stickier than typical headline spikes because markets are pricing both barrels and the cost of moving barrels given the entire Middle East region is engulfed in the conflict,” said Charu Chanana, chief investment strategist at Saxo. “Even without a full shutdown, higher war-risk premia, rerouting and insurance repricing can keep crude and freight costs elevated.”

Analysts say Iran has long treated the strait as a strategic pressure point, though a full prolonged blockade is considered unlikely as Tehran relies on the same route for crude exports and wider trade.

“While labeled the ‘mother of all disruptions,’ this posturing reveals a critical paradox,” said Naveen Das, senior crude analyst at Kpler. “Unlike Saudi Arabia and the UAE, which have operational bypass pipelines, Iran’s Goreh-Jask pipeline has seen minimal usage, leaving Tehran almost entirely dependent on the Strait for its own exports.”

Iran—the fourth-biggest oil producer in the Organization of the Petroleum Exporting Countries—pumps roughly 3.3 million barrels a day of crude oil. China is its largest buyer, importing more than 80% of its shipped oil.

In the wake of the conflict, key members of the OPEC+ alliance agreed to a larger-than-expected increase of 206,000 barrels a day in oil production for April, a move that analysts say reflects the need to address geopolitical risks while also safeguarding its limited spare capacity. However, analysts caution that a prolonged closure of the Strait of Hormuz would physically constrain OPEC’s ability to deploy its spare capacity.

Write to Giulia Petroni at giulia.petroni@wsj.com

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