The ban, which remains in effect through Nov. 6, also covers the Strategic Petroleum Reserve (SPR) that currently holds 545 million barrels of oil in underground salt caverns at four locations along the coasts of Texas and Louisiana.

The emergency stockpile was created by Congress in 1975 after the Arab oil embargo and is intended to be a cushion against a disruption in foreign oil imports.

The reserve's salt caverns are located 2,000 to 4,000 feet below the surface, offering the best security and the most affordable means of storage. Cavern storage costs can be one-tenth of those for storage in above-ground tanks, according to the Energy Department.

The caverns range in size from 6 to 30 million barrels in capacity. The typical cavern holds 10 million barrels and is cylindrical in shape, with a diameter of 200 feet and a height of 2,000 feet.

A typical cavern is large enough for Chicago's Sears Tower to fit inside with 170 feet to spare, the department said.

The U.S. consumes about 19.5 million barrels of petroleum a day, and imports account for about 60 percent of those supplies.

The Bush administration is expected to decide soon on whether to boost the reserve to its fully capacity of 700 million barrels.