June 2 (Bloomberg) -- Iran, OPEC's second-largest oil producer, increased the number of tankers idling in the Persian Gulf to at least 14, indicating it may be storing more crude, ship-tracking data show.

Iran has at least 14 very large crude carriers, or VLCCs, floating near Kharg Island, a loading facility. In April, there were 10, holding at least 20 million barrels of oil, people familiar with the situation said at the time. Shipbrokers also reported that Iran hired three more tankers, which have been near Kharg Island for at least two weeks.

Iran has a glut of its sulfur-rich crude because refineries that can process the fuel shut down for maintenance. The discount on Iranian Heavy crude compared with Oman and Dubai petroleum has widened for three consecutive months to its biggest since January 2007, according to data compiled by Bloomberg. Earnings from supertankers more than tripled from April to May.

The use of vessels for storage has been a ``component of the rise'' in rental rates, Mathieu Philippe, a tanker broker at Barry Rogliano Salles in Dubai said by phone today. Rates have also been bolstered by record crude output by the Organization of Petroleum Exporting Countries and reduced demand for single-hull tankers that increase the risk of oil spills, he said.

The 14 supertankers are capable of storing as much as 28 million barrels of oil, equal to about 12 days of Iran's total output. The three tankers hired by National Iranian Tanker Co. can store another 5 million barrels between them.

Iran will start cutting the amount of crude stored on tankers this month, Energy Intelligence reported on its Web site May 29, citing Hojatolla Ghanimifard, executive director of international affairs at the National Iranian Oil Co.

Sulfur Content

Ghanimifard didn't immediately respond to phone calls to his office seeking comment on May 29 and today.

Soroush and Nowruz crudes contain about 3.5 percent sulfur. Syria's Souedieh, at 3.9 percent, is the only grade in the Middle East with more, according to data from New York-based Energy Intelligence Group. Previous buyers of the oil include SK Corp., South Korea's biggest refiner, and Reliance Industries Ltd., India's biggest company by market value.

The following VLCCs are all able to ship, or store, at least 2 million barrels of crude. Their expected arrival and when they were last seen are from AISLive ship-tracking data. It normally takes 24 hours to 48 hours to load a cargo of crude and set sail.

The data do not show how many tankers are fully loaded.

Ship name      Destination    Arrival:       Last Seen
Noor           Kharg Island   Dec. 15, 2007  May 31
Najm           Kharg Island   Feb. 20        June 2
Noah           Kharg Island   April 2        June 2
Huwayzeh       Kharg Island   April 3        June 2
Hoda           Kharg Island   April 14       June 2
Nabi           Kharg Island   April 24       June 2
Damavand       Kharg Island   April 11       May 31
Daylam         Kharg Island   April 23       June 1
Hadi           Kharg Island   May 6          June 2
Delvar         Kharg Island   May 14         June 1
Nesa           Kharg Island   May 14         June 1
Harsin         Kharg Island   May 12         May 31
Hamoon         Kharg Island   May 16         June 2
Hirmand        Kharg Island   May 27         June 1

Following is a table of crude tankers hired by National Iranian Tanker Co., according to reports from Athens-based, Optima Shipbrokers or Paris-based shipbroker Barry Rogliano Salles. They have been stationed at Kharg Island for at least a week:

Ship name        Capacity       Expected       Last Seen
                 (Barrels)      Arrival
Astipalaia       2 million      April 26       May 31
Safwa            2 million      May 13         June 2
Eastway          1 million      May 19         June 1

To contact the reporter on this story: Alaric Nightingale in London at Anightingal1@bloomberg.net

Last Updated: June 2, 2008 08:06 EDT