BANDAR ABBAS, Iran — The hulking tanker Neptune was floating aimlessly this week in the warm waters of the Persian Gulf, a fresh coat of black paint barely concealing its true identity as an Iranian ship loaded with hundreds of thousands of barrels of oil that no one is willing to buy.

The ship’s real name was Iran Astaneh, and it was part of a fleet of about 65 Iranian tankers serving as floating storage facilities for Iranian oil, each one given a nautical makeover to conceal its origin and make a buyer easier to find. The Neptune had been floating there for a month, and local fishermen said there were two even larger tankers anchored nearby.

Iran, faced with increasingly stringent economic sanctions imposed by the international community to force it to abandon any ambitions to develop nuclear weapons, has been reluctant to reduce its oil production, fearing that doing so could damage its wells. But Iran has insufficient space to store the crude it cannot sell. So while it furiously works to build storage capacity on shore, it has turned to mothballing at sea.

“We have never seen so many just waiting around,” said Rostam, a fisherman and smuggler who regularly works these waters.