Russia and China have said they will not join any embargo of Iranian oil.  For Russia the reason is simple: “…we are not consuming Iranian oil at all!”-Sergei Shmatko, Energy Minister of Russia

You’d think the leaders of Canada, the U.K. and U.S. (the countries pushing for an embargo of Iranian oil) would already know that.

For China the reason is personal: “Iran is a very important supplier of oil for China. I believe there would be a massive conflict between America’s prohibition from, and China’s interest in, the Iranian crude. China won’t certainly do what the United States says!” He Jun, Anbound Information Consultancy

Put it another way; China is willing to go to war over it!