From Dec. 5, the European Union will be prohibited from importing Russian crude oil. Insurance companies covering sea-born oil shipments will no longer be able to cover vessels carrying Russian crude anywhere in the world. Moscow will then face a choice: decrease production at home by capping wells or assemble vessels outside the West to offload the crude to other buyers. The sanctions could take as much as two million barrels off the global market, raising energy prices.

The G-7, working with the EU, is scrambling to finalize a fix to avoid that price surge. It has been working on a plan that would permit EU and U.K. vessels to transport Russian crude as long as the oil is bought at a certain price. Whether this gambit would work or not is less clear.