Shell: Gulf oil sheen dissipating; source unknown

Shell says an oil sheen off the coast of Louisiana has broken up and is dissipating.
The source of the sheen in the Gulf of Mexico remains unknown. The sheen, which was about a mile (1.6 kilometers) wide and 10 miles (16 kilometers) long, was spotted Wednesday afternoon in the area of two Royal Dutch Shell PLC production platforms. The oil giant said it's confident the oil didn't come from its operations.
The company was aiding U.S. agencies by using two remotely controlled underwater vessels to check for any leaks in plugged wells or naturally occurring seepages from beneath the sea floor. The company said the surveillance would continue Thursday and Friday.
Shell estimates the sheen at six barrels of oil, or about 252 gallons (953 liters).
The Coast Guard did not immediately comment.