Iran has exhausted the offshore oil reserves that sustained its sales to China during the war, according to one energy-data firm, eliminating a critical financial cushion as a U.S. naval blockade intensifies pressure on its struggling economy.

The reserves were fully depleted by mid-October, according to analysts at energy data company Kpler, although other trackers offered varying estimates of the remaining supplies, The Wall Street Journal reported on Thursday.

“There’s no more oil to discharge to China anymore,” Homayoun Falakshahi, Kpler’s head of crude-oil analysis, said.

The depletion threatens a major source of government funding as Tehran confronts soaring inflation, widespread shortages, and a weakening currency. Oil sales account for 30% to 40% of Iranian government revenue and are its largest source of foreign exchange, according to Falakshahi.

U.S. Central Command said Saturday that the blockade had deprived Iran of at least $25 billion in oil revenue, limiting its ability to rebuild damaged factories and replenish its weapons stockpiles.

U.S. actions have “imposed devastating costs on Iran’s security apparatus,” Adm. Brad Cooper, commander of U.S. Central Command, said.

Meanwhile, oil shipments from other Middle Eastern countries have exceeded prewar levels as U.S. protection helps non-Iranian tankers transit the Strait of Hormuz, the Journal reported.

“It looks like the U.S. gamble is that the economy will either push the regime back into negotiations to accept a nuclear deal, or will spark protests internally which the regime will face challenges containing,” Falakshahi said.

Iran built its offshore oil stockpile through a system designed to evade sanctions by moving crude to waters near Malaysia and Singapore.

There, tankers transferred crude to other vessels bound for Chinese refineries, making the shipments harder to trace and creating a floating storage network.

At the start of the war in February, Iran had about 135 million barrels of oil stored overseas, according to Kpler. The stockpile was potentially worth at least $10 billion after oil prices surged.

The reserves began shrinking rapidly after the United States imposed a blockade in April. Iran replenished its stockpile when Washington lifted the blockade during peace negotiations in mid-June, but supplies declined again after restrictions resumed in mid-July.

The replenished stockpile peaked at nearly 90 million barrels before dropping below 1 million barrels by Oct. 5 and eventually running out, according to Kpler.

Other energy trackers agreed that supplies had declined sharply but offered different estimates of the remaining stockpile.

Emma Li, an analyst at energy tracker Vortexa, estimated that about 6 million barrels of Iranian crude remained near Singapore as of Oct. 9. She said Chinese refineries were increasingly turning to suppliers in Brazil and West Africa.

United Against Nuclear Iran, an advocacy group, estimated that Iran’s oil exports fell to nearly zero in August and September, while floating reserves in Southeast Asia likely declined to 10 million barrels or less by early October.

“They’ve got to be hurting,” Charlie Brown, a researcher with United Against Nuclear Iran, told the Journal. Although he could not confirm that the reserves were exhausted, he said “it seems likely to be well on the way to close to zero.”

Iran could continue receiving payments from earlier oil sales because Chinese purchases typically take about two months to settle, analysts said. However, overland shipments and other alternatives cannot replace the volume previously transported by sea.

Tehran has resisted the blockade’s pressure for more than six months by storing crude in aging tanks and trucking supplies to neighboring countries. Nevertheless, its currency has lost about a third of its value against the dollar since early July, fueling inflation.

“Is it working? Yes, it’s working,” said Iman Nasseri, senior vice president of Middle East and Asia at FGE NexantECA, who previously worked in the research arm of Iran’s oil ministry.

Nasseri cautioned, however, that Iran’s government has survived previous economic crises.

“Let’s wait another year and see if the system can stand,” he said.

Iranian officials maintain that the country can withstand the restrictions.

At an International Monetary Fund meeting in Bangkok last week, Iranian central bank Gov. Abdolnaser Hemmati said the country’s economy “has demonstrated very good resilience, and the claim that Iran’s economy is collapsing is nothing more than an illusion.”