Iran, OPEC’s second-largest crude producer, has at least three supertankers idling in the Persian Gulf, as oil prices decline five weeks before the group’s next meeting, vessel-tracking data show.

The tankers, each bigger than the Chrysler Building, have been almost stationary for at least four weeks, according to data from the ships collected by AIS Live Ltd. The depth of the 2-million-barrel vessels sitting in the water indicates they are loaded. The amount of oil stored may expand because signals from two more idled tankers shows they are partially loaded or empty.

If full, the three tankers’ combined capacity of about 6 million barrels is equal to 19 percent of all the crude the U.S. Energy Department estimates is stored in Cushing, Oklahoma, the pricing point for benchmark West Texas Intermediate oil.

As Iran’s cargoes sit, oil companies and banks are selling crude stored on tankers into the market. The number of ships involved in the “contango” trade, named after the term used to describe a market where future commodity prices are higher than today, declined 16 percent last month, according to data from London-based E.A. Gibson Shipbrokers Ltd. The amount of crude tied up in storage fell 25 percent last week, Morgan Stanley said in a Feb. 7 report.