In a bid to circumvent crippling international sanctions, Iran has been routinely switching off satellite tracking systems on its sea-bound oil tankers, The Washington Post reported.
Citing unnamed US officials, the newspaper said the practice has been going on for more than a month.
US officials and industry analysts describe it as a cat-and-mouse game with Western governments seeking to enforce sanctions on Iranian exports, the report said.
The unusual tactic was begun in early April and affects a quarter of Iran's tanker fleet, according to the International Energy Agency (IEA), which has been monitoring the practice, the paper noted.
The move, a violation of maritime law, is only modestly effective in hiding tankers as they ply the oceans in search of open ports and willing buyers, The Post said.
But it underscores Iran's precarious position as it faces ever-tighter Western restrictions against its oil industry, the paper noted.
Iran relies on oil exports for around two-thirds of its foreign currency earnings.
The Islamic republic is the second biggest exporter in OPEC, after Saudi Arabia. Last year, it exported some 2.6 million barrels per day of the 3.5 million bpd it pumped out of its huge reserves.
The United States and the European Union have imposed their economic sanctions on Iran to pressure it over its disputed nuclear programme.
The West and the UN's International Atomic Energy Agency suspect the programme includes a drive to develop the capability to make atomic weapons, despite Iran's repeated denials.