gCaptain has an interesting discussion of the potential economic consequences of offshore drilling beyond the 200 mile EEZ. It seems UNCLOS has a provision (Article 82) that a UN agency is owed a percentage of the revenue from such drilling.
There is apparently some ambiguity in the treaty, in that it is not clear if the fee is to be based on gross or net revenues, and it is also unclear where continental shelves end, but apparently the existing provisions make it possible to claim sea floor as deep as 5,000 meters, far deeper than what I thought of as continental shelf, and an area as large as Africa (which is really much bigger than it looks on a Mercator projection, roughly four times the land area of the United States).
There is also a chart (map) of where continental shelf claims are currently being made. There are number of potentially “interesting” (eg contentious) areas being claimed.
—There are claims off Antarctica.
—There are claims between Argentina and the Falklands.
—Claims in the Arctic.
—Claims in the South China Sea. I wonder if the Chinese don’t hope to avoid fees all together by claiming it is theirs under a different status.