The width of the continental shelf varies significantly. It is quite common for an area to have virtually no shelf at all. The largest shelf - the Siberian shelf in the Arctic Ocean - streches to 900 miles in width. The average width is about 50 miles. The depth of the shelf also varies. It may be as shallow as 100 feet or as deep as 2000.
The continental shelf is by far the best understood part of the oceans on account of its relative accessibility. Virtually all commercial exploitation, such as oil and gas extraction, from the sea takes place on the continental shelf.