Oil is pouring out of the Persian Gulf at the fastest rate since the start of the Iran war, even as a recent uptick in attacks threatens the flow. The cost of getting it out is eye-watering: Up to $40 million for a multiday trip.

For Gulf oil producers, it is worth it. Leaving the oil stranded is still economically worse than taking on the freight cost and selling oil at thinner margins.

So producers inside the Gulf have turned to hiring very large crude carriers, known as VLCCs, to complete a perilous journey known as a "shuttle run." Carriers enter the Persian Gulf via the Strait of Hormuz, load at ports there, exit from the strait, then transfer the oil to another vessel waiting just outside of the waterway.

These are the new economics of the Strait of Hormuz, where a wartime gold rush has pushed producers to swallow record freight costs just to keep crude moving; shipowners are reaping some of the best returns the industry has seen in decades; and the sailors who make the dangerous crossing are being paid like never before.

Those financial rewards comes with substantial risks. After several days of calm, seven ships have been hit since Sept. 28, according to the U.K. Maritime Trade Operations, which is affiliated with the Royal Navy. A few of those tankers have been identified as shuttle tankers, according to maritime security firms.

Shuttle runs weren't necessary before the war. But when Tehran started hitting commercial vessels in the strait, buyers in Asia and elsewhere became reluctant to send their own ships to pick up oil from inside the Gulf. Now oil producers are shelling out between $30 million to $40 million for a round trip in and out of Hormuz-or $15 to $20 a barrel excluding insurance, according to shipbrokers.

"For many shipowners, the current market is generating revenues at levels rarely seen in the industry's recent history," said Dimitris Maniatis, founder and chief executive officer of maritime risk company Marisks.

Ferrying oil directly from the Persian Gulf to global markets is also more expensive than ever, contributing to the appeal of shuttle runs. The cost of hiring an oil supertanker to sail from the Persian Gulf to China topped $1.2 million a day in late September. On the eve of the war, that cost was about $231,400 a day, according to maritime data provider Clarksons Research. In early January, it cost less than $40,000 a day.

The shuttle-run bonanza is trickling down to individual sailors. Those willing to perform the war-zone trips-many from India, the Philippines and China-are being lured with payouts worth two or three times their typical monthly salary. One Shandong-based ship staffing company is even offering as much as $25,000 per round trip as reward, according to seafarers and recruitment advertisements seen by The Wall Street Journal. For oilers and cadets, the $25,000 could represent more than a year of wages.

An executive at the company said it is currently using the $25,000 offer to recruit oilers and ordinary seamen for a VLCC that will go into the Persian Gulf on a rolling basis.

"Given the millions being made at the moment, that's absolutely nothing to the shipowners," said Richard Matthews, director of consulting and research at shipbroker E.A. Gibson.

Expanding shuttle fleet

The demand for shuttle runs exploded last month after drone attacks shut Saudi Arabia's bypass East-West pipeline. To keep exporting oil, the kingdom's flagship oil company Aramco has joined its regional peers in employing shuttle tankers.

The core fleet of tankers doing these shuttle runs-those that have done four or more runs of unloading Gulf-loaded cargoes to ship-to-ship transfer zones off the ports of Fujairah, Sohar and Shinas-has grown from 30 vessels at the end of August to 39 now, according to Claire Jungman, director of maritime risk and intelligence at ship-tracker Vortexa. Saudi Arabia's share of shuttle tankers is rising fast, Jungman said.

The trade is currently dominated by a few shipowners including South Korea's Sinokor and Greek billionaire George Prokopiou's Dynacom. However, smaller shipowners including owners of older vessels that used to ferry Venezuelan and Russian oil have joined the trade, said shipbrokers. If these vessels manage to get insurance and become a total loss, shipowners can claim back the full value of the ship, which may be a better economic proposition than eventually having to scrap the vessels, they said.

Getting insured can prove difficult.

"When we see these ships coming into the insurance market, we assess the operator's capability. Have they done this trade before? Who's going to run the ship? Do they have connections in the market to repair these ships if they are hit?" said Sundeep Khera, head of marine at Beazley, a global insurer.

Even with the partial restart of the East-West pipeline, Saudi Arabia will likely still rely on shuttle runs in the near future, said Anoop Singh, the head of global shipping research at commodity broker Oil Brokerage.

Gradually, more crude will go through the pipeline to the Red Sea port of Yanbu. But Saudi Arabia will still need to ship those barrels north up to the Suez Canal, meaning a much longer journey than through the Strait of Hormuz. "Saudi Arabia cannot find enough tankers if it wants to push three million barrels a day of crude exports from Yanbu up north to the Suez and then around Africa into markets in East Asia," Singh said. He reckons that ultimately, two-thirds of the Saudi oil flows will still go through Hormuz.

A dangerous journey

Behind the high reward are high-and real-risks. In the past two weeks alone, nine commercial vessels were attacked near the Strait of Hormuz, resulting in two seafarer injuries and one death, according to the International Maritime Organization and the U.K. Maritime Trade Operations Center, which is affiliated with the Royal Navy.

Two seafarers on two different VLCCs shared their recent experience with The Wall Street Journal. One of them, the first mate on a shuttle tanker, said he had been in and out of Hormuz twice in the past month. Both trips were at night-with the windows shut and lights turned off.

During each transit, his vessel lost GPS signal for hours and navigated using old-school methods such as using radar signals to calculate the angle and distance relative to islands and headlands to determine the vessel's position.

He said that half of the crew quit after completing just one round trip, but the ship management company had no problem replacing them after promising extra pay. He was paid three times his monthly salary for the days transiting in the conflict zone, he said.

Another crew member on a separate VLCC said he knew that Iran could hit the vessel with drones, but he didn't anticipate the risk of being hit by missiles.

He was paid double his daily wages.