Ship industry sources gave varying estimates on how much oil Iran was storing at sea, but all said the volume was higher.
Data from maritime intelligence publisher IHS Fairplay estimated 10 of Iran's supertankers, each able to carry up to 2 million barrels of crude, were storing oil, together with one smaller tanker able to carry up to 1 million barrels.
The data showed a further two supertankers were also probably deployed on floating storage, based on the length of time they were stationary, meaning as much as 25 million barrels in total.
The vessels, all belonging to Iran's top tanker operator NITC, were located close to the Iranian oil terminals of Assaluyeh, Kharg Island and Bahregan, the data showed.
Another ship industry source estimated 17 NITC vessels were storing crude oil, mainly on supertankers, while another said 15 tankers were storing crude oil around Iran, with volumes close to 30 million barrels.
Last year Iran's floating storage was estimated to have reached at least 33 million barrels before buyers were found.