Royal Dutch Shell says a substantial amount of oil has leaked into the North Sea from the company's platform off the Scottish coast.

Shell estimated Monday that about 1,300 barrels 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.

Shell said the oil will disperse naturally and is not expected to reach the shore.

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.”