Most of the shipments were to East Coast refineries from loading points in the Gulf of Mexico.

Administration officials said that the oil was sold in large lots, most of them 500,000 barrels or more, and the dozen or so oil companies and traders that bought them found it faster and more economical to move the oil on 500,000-barrel capacity ocean-going tankers rather than on American-owned coastal barges. With only a couple of exceptions, the coastal barges tend to hold 150,000 barrels or less.

Clark Stevens, a White House spokesman, said that the administration tried to accommodate the domestic maritime industry by lowering the minimum lot size and by considering individual waivers. The administration would have preferred to use American ships but they were not available, he said.

In an e-mailed statement, he said: “Due to the volumes requested by the purchasing companies and the focus on getting this oil to U.S. markets as quickly as possible, the Department of Homeland Security — working with the Maritime Administration and the Department of Energy — determined that individual Jones Act waivers were appropriate since the U.S. fleet had only small barges available, and the buyers bid on the basis of larger, more efficient tankers.”

OSG, a shipping company based in New York, transported oil for three of the oil companies that bought crude from the petroleum reserve. It moved one shipment on an American-flagged barge and three on large tankers that are registered in the Republic of the Marshall Islands.

Morten Arntzen, the company’s chief executive, said that the United States was not an oil-exporting country and therefore did not have the capacity to move large shipments of oil on short notice. He said that a relatively large sale from the petroleum reserve was a rare event and that it did not make sense for domestic oil shippers to maintain fleets of tankers.