The Trump administration says large volumes of oil are slipping through the Strait of Hormuz. The trackers whose job it is to count the world’s oil shipments see much less Energy Secretary Chris Wright said last week the U.S. military had helped ship over 15 million barrels* of crude and oil products out of the waterway last Tuesday. He put the average oil exports through the strait over a seven-day period at more than 8 million barrels a day. Earlier this month, Wright said the seven-day average stood at around 9 million barrels a day. The count from commercial ship trackers tells a different story, with estimates ranging from roughly 2 million to 6 million barrels a day. Industry figures on the amount of crude oil and oil products being loaded onto ships in the Persian Gulf and delivered to buyers don’t corroborate the U.S. claims.

There are lots of reasons the numbers can diverge. Many ships are crossing the strait at night with their transponders off, making them hard to track by radio signal or satellite imagery. Big tankers can carry 2 million barrels apiece, so missing one or two can make all the difference. Measurement periods also make a big difference, as do assumptions about how full ships are when they cross. Wright has said private data firms are undercounting ships that move covertly through the waterway. Still, a persistent gap remains between Washington’s estimates and what the market can independently verify. “What’s remarkable is how similar tanker trackers’ numbers are. You’d expect someone to have figured out a way to validate the White House numbers if there was a way,” said Rory Johnston, founder of Commodity Context, an oil-market research firm. “As of yet, I haven’t seen anyone do it.” U.K. Maritime Trade Operations, which is affiliated with the Royal Navy, cited U.S. Navy data in a report over the weekend that said the U.S. facilitated 74 transits through Hormuz from Thursday through Saturday, or around 25 transits a day on average. The numbers don’t specify how many were oil tankers or how many barrels they carried. The UKMTO hasn’t independently verified the U.S. data, but believes it to be accurate, a person familiar with the matter said.

“Commercial traffic through the Strait of Hormuz remained at reduced levels,” UKMTO said in its report. “Independent tracking data indicated suppression with single-digit numbers transiting in both directions.” The discrepancy echoes the oil market’s familiar bane of “missing barrels”—volumes that show up in one set of figures but can’t readily be accounted for elsewhere. Such debates ultimately get settled in physical markets, where the oil is either available or it isn’t. So far, markets are relatively relaxed, with benchmark Brent crude futures elevated around $90 a barrel but well off their wartime highs, indicating the market isn’t desperate for supplies. Earlier in the war, a yawning gap emerged with physical market cargoes priced well above Brent futures, signaling immediate supply pressure and traders’ optimism that the war would be over soon. That gap—once as large as $36 a barrel—has narrowed to less than $6 in recent months, according to Argus Media, a price-reporting agency. Futures prices for oil that flow out of the Gulf, such as a grade of crude known as Dubai, have come down from $160 a barrel in late March to around $97 a barrel Friday, according to Argus Media. But the discrepancy does matter in terms of setting expectations for oil traders and for judging who is winning the economic war of attrition that Washington and Tehran are fighting, with oil as a key weapon.

The U.S. Navy for months has successfully guided some tankers through a protected route along the Omani side of the strait, eroding Iran’s control and easing the pressure on global oil markets. Iran responded in July by attacking ships using the route, sinking an agreement to open the waterway. On Monday, it threatened to fine or detain 46 ships it said had broken its rules for transiting the strait. The United Arab Emirates and Saudi Arabia have also managed to route millions of barrels a day around the blockade by piping them across the desert to the Gulf of Oman or the Red Sea. Mohsen Rezaei, a top Iranian official, said late Sunday that those routes will be threatened if the U.S. continues its campaign of squeezing Iran’s economy. Kuwaiti, Iraqi and Emirati officials said some tankers are getting through under separate arrangements with Iran, meaning not all of the traffic is moving under U.S. protection. Ship trackers say roughly a third of the vessels that have transited the strait during August have used the Iranian-administered route along the northern reaches of the waterway.

With the war knocking out large volumes of supply, oil prices and the global economy are unusually sensitive to how much crude might come to market. Kpler, a ship-tracking firm, estimates that exports of crude and oil products through Hormuz have run at about 2.3 million barrels a day so far in August, down from 4.9 million barrels a day in July. Huax, another tracker, puts a current range for crude and refined products at 2 million to 5 million barrels a day. Johnston’s latest seven-day average of confirmed transits is about 4 million barrels a day, though he expects that to be raised to 5 million to 6 million as ships that made dark crossings turn their transponders back on after they clear the strait and their voyages can be reconstructed. Data from Vortexa, another tanker tracker, runs closer to the administration’s numbers but only across a short window. It says its seven-day average recently peaked at 9.2 million barrels a day. But its 28-day moving average, which the company says is more representative because it smooths out short-term spikes and volatility, remains at around 6 million barrels a day, underscoring how dramatically the picture can change depending on the dates selected.

The biggest problem for trackers is that many tankers are going dark. Ships normally broadcast their identity, position, speed and direction through AIS transponders, a radio-based automatic identification. But with many vessels switching off their AIS before crossing Hormuz, analysts have to reconstruct the voyages using satellite imagery and other clues. “So many ships are transiting dark, which makes it difficult to tally total tanker movements in real time,” said Bridget Diakun, maritime intelligence and research director at Lloyd’s List Intelligence. “We are partially waiting for AIS to come back on, but we also need to wait for satellite imagery to be available to validate sailings through Hormuz.” Satellites can help identify ships at berths in the Gulf and then in areas beyond the strait where ship-to-ship transfers occur. But satellite imagery just captures points in time and isn’t great for tracking the chokepoint itself, as it misses the bulk of the movements at night, she said. Detecting a ship doesn’t settle how many barrels moved. Analysts need to establish whether it was laden with oil or sailing empty. A very large crude carrier, or VLCC, is capable of holding roughly 2 million barrels, but that doesn’t mean it is full. The U.S. military has wider sources of information given its active presence around the Gulf, advanced sensors and communications with ships in transit. “I can’t get to 10 million barrels a day from the vessel and cargo picture available to me,” said Arsenio Longo, the founder of Huax. “The military may well be seeing vessels through radar, aircraft or other surveillance that commercial feeds miss.”

There is another way to check: Oil can’t move through the strait if it isn’t first put on tankers somewhere in the Persian Gulf. Those figures also don’t line up with the U.S. transit claims. LSEG puts crude and product loadings inside the Persian Gulf at about 4.4 million barrels a day in July and 1.9 million so far in August. The data provider says Iraq, which lacks a major bypass route, loaded just 1.1 million barrels a day so far this month, less than a third of prewar levels, while Kuwait loaded 0.5 million, one-fifth of its prewar rate. Kuwaiti officials say they are exporting more, around 1 million barrels a day. The ultimate check on Washington’s numbers is whether the barrels ultimately surface somewhere. Even if tankers disappear while crossing Hormuz, much of that oil should eventually show up in data on barrels unloaded to buyers or middlemen. So far, the U.S. government’s claimed volumes aren’t fully showing up in other countries’ import volumes. According to LSEG data, an average of 11.6 million barrels per day of Middle Eastern crude and refined products have been or are scheduled to be discharged in Asia. That number includes oil exports routed around Hormuz by pipeline, not just barrels escorted through the chokepoint.