• The latest oil tanker seizure of the containership MSC Aries over the weekend marked at least the sixth vessel recently hijacked by Iran and its proxies.
• Iran is unlikely to ever close the Strait of Hormuz to tanker traffic given the importance of exporting its oil to China.
• But the tankers it hijacks are likely to be held for a long time, according to Samir Madani, co-founder of Tankertrackers.com. "They want to keep the waters in a constant state of chaos," he says.

The containership MSC Aries seized by Iran over the weekend marked at least the sixth vessel hijacked by Iran and its proxies in response to the Israel-Gaza war, and it's adding to the challenges to longstanding freedom of navigation principles that maritime shipping relies on.

Before this weekend's tanker seizure, the last vessel Iran hijacked was the St. Nikolas on January 1. According to U.S. Naval Forces Central Command, that brought the total number of vessels being held to five, and over 90 crew members hostage. Previous to that, the Iranian-backed Houthis hijacked The Galaxy Leader on November 19.

The latest development has shipping and energy experts bracing for a long-term timeline of uncertainty.

"Iran is in this for the long haul," said Samir Madani, co-founder of Tankertrackers.com, an independent online service that tracks and reports crude oil shipments in several geographical and geopolitical points of interest.

The MSC Aries was identified by Iran as having a link to Israel. The containership has a carrying capacity of 15,000-TEUs (twenty-foot equivalent containers). MSC leases the Aries from Gortal Shipping, an affiliate of Zodiac Maritime, which is partly owned by Israeli businessman Eyal Ofer.

MSC declined to comment directly to CNBC.

In a statement released by MSC on Wednesday, it said the crew members were safe and discussions with Iranian authorities were underway to secure their earliest release and to have the cargo discharged.

Madani said he does not expect a quick release. "They will hold the MSC Aries for a long period. Iran has been holding some tankers for about a year, if not longer now," he said.

According to Tankertracker information, Madani said the vessel is being held in the Khuran Straits, not too far from three other tankers Iran hijacked: the Advantage Sweet, Niovi, and St. Nikolas.

As the U.S. considers more sanctions against Iran in response to its recent attack on Israel, Iran has been using the hijacked ships as a means of sanctions retaliation.

"Iran has already seized the Kuwaiti oil that was onboard the Advantage Sweet and has been loaded onto their VLCC supertanker the Navarz. Iran chose to do this as a way to compensate for sanctions," Madani said.

While the Niovi was empty at the time of the seizure, the St. Nikolas is filled with a million barrels of Iraqi oil.

Treasury Secretary Janet Yellen said on Tuesday that the government may do more to prevent Iran's ability to export oil despite U.S. sanctions. China's purchases of Iranian oil in recent years have allowed Iran to keep a positive trade balance.

According to the U.S. Energy Information Agency, China, the world's largest importer of crude oil, imported 11.3 million barrels per day of crude oil in 2023, 10% more than in 2022. Iran ranked second in oil exports to China behind Russia. Customs data indicates that China imported 54% more crude oil (1.1 million b/d) from Malaysia in 2023 than in 2022, with industry analysts speculating that much of the oil shipped from Iran to China was relabeled as originating from countries such as Malaysia, the United Arab Emirates, and Oman to avoid U.S. sanctions.

The markets continues to assess the risk of further escalation in the military tensions between Israel and Iran, which could lead to a disruption in the Strait of Hormuz, through which about 30% of the world's seaborne oil passes, according to JPMorgan. On Tuesday, oil edged higher amid talk of sanctions.

An Iranian blockade would supercharge oil prices, but the risk is low given that the strait has never been closed off despite many threats by Tehran to do so over the past four decades, according to JPMorgan.

"They can't close the Strait of Hormuz, but they can do significant damage to energy infrastructure, to vessels in the region," RBC's head of global commodity strategy and Middle East and North Africa research, Helima Croft, told CNBC on Monday, referring to Iran's capabilities.

"While I can't imagine Iran would want to fill up their anchorage with vessels, they want to keep the waters in a constant state of chaos," Madani said. But with a closure, he said, "They would shoot themselves in the foot since their biggest client is China."

Andy Lipow, president of Lipow Oil Associates, says the closure of the Strait of Hormuz would result in a spike of Brent crude oil prices to the $120 to $130 range. "This would strain ties with China and India who purchase a significant amount of Persian Gulf oil to meet much of their energy demand."

Lipow also said Iran might be reluctant to shut the waterway for fear of antagonizing Saudi Arabia, Kuwait and Iraq, who depend on the strait being open for most of their oil exports. The bigger immediate fear in the oil market, he said, is that the attack by Iran on Israeli territory leading to a counterattack by Israel on Iran damaging oil-producing and exporting facilities.

Kevin Book, managing director of ClearView Energy Partners, says the markets need to keep an eye on sanctions from both the US and UN potentially.

In a note to clients, ClearView highlighted that the House of Representatives added several Iran sanctions bills to its calendar for consideration this week, under suspension rules, including new sanctions on Iranian oil exports to China. Book said the House was considering 11 bills in all in response to Iran's attack on Israel.

"We think most if not all bills could garner (notionally) veto-proof bipartisan support," the note said. "Passage requires a two-thirds majority of all members present and voting."

Israel has also asked the U.N. to reinstate multilateral sanctions lifted by the Iran nuclear deal, but for this to happen, France, Germany and the U.K., parties to the nuclear deal, would have to agree. "There are many risks unfolding. The forest is on fire," Book said.