Fears of an oil spill in the Gulf of Mexico have triggered a slide in the shares of energy giant Royal Dutch Shell.
The alert came after the Anglo-Dutch company notified the authorities of a light sheen on waters near to its production facilities.
It is "confident" that the oil sheen has not originated from the wells in its Mars or Ursa projects, but out of "prudent caution" has sent a response vessel to investigate further.
With BP's Deepwater Horizon disaster of 2010 fresh in the minds of investors, shares in the company dropped as much as 5% before recovering after Shell said all its operations in the area appeared to be operating normally.
As well as sending the vessel, Shell requested flights to monitor the sheen, which measures one mile by 10 miles.
Shell said: "A thorough inspection to date of Shell assets reveals operations in the area are normal with no sign of leaks. We have also confirmed there are no well control issues associated with our drilling operations in the area."
The Deepwater Horizon rig explosion killed 11 workers and affected hundreds of miles of coastline after an estimated 4.9 million barrels of oil poured into the sea.