Royal Dutch Shell said Tuesday that oil continues to leak into the North Sea from the company's platform off the Scottish coast at a rate of two barrels a day.

A Shell spokesman said the company does not know when the leak will be stopped, but that most of the visible oil slick has already been dispersed by waves and is not expected to reach the shore.

Shell estimated Monday that about 1,300 barrels have spilled from its Gannet Alpha rig, off Aberdeen. The company says the spill covers an area of about 31 by 4.3 kilometers at its widest point.

Royal Dutch Shell said the leak began last Wednesday, and environmentalists criticized the oil company for waiting several days before announcing the spill.

The spill is considered small compared to the devastating BP oil slick last year in the Gulf of Mexico. But a Scottish environmental charity called the spill “deeply disturbing.”