From Fox News:

The Obama administration has, according to senior officials, begun circulating a list of potential sanctions against Iran, including limits on oil exports and tighter restrictions on access to international credit as it seeks ways to intensify pressure on the regime’s feared pursuit of nuclear weapons.
Officials stressed there is no draft of potential sanctions and many ideas are being discussed. Talks are limited to a close-knit number of nations as the US seeks to built momentum for a future package of sanctions. One official involved in the process said the U.S. is “intensely” discussing the contours of a sanctions package with members of the P5 +1, but that China is not yet part of the discussion.
The P5+1 includes the U.S., Russia, France, Great Britain (the permanent members of the U.N. Security Council) and China. The official said China is being kept at arms-length for now because the U.S. wants to first iron-out a package of sanctions and then see what China might be prepared to tolerate.
The administration strategy assumes China will use its Security Council vote to [veto] sanctions against Iran. But the US believes China can be persuaded to abstain, a move that would allow the sanctions to go proceed. All other permanent members of the Security Council – France, Britain, Russia and the U.S. support a sanctions package, the official said.