You probably would be interested in this from an article on CNNmoney.com, March 30, 2012...
U.S. TIGHTENS OIL SANCTIONS ON IRAN
Earlier this month the State Department said Japan and the EU and a number of a number of other countries have reduced their purchases of Iranian oil enough to avoid sanctions. If China, India and South Korea and 10 other nations don't follow suit by June 28, they could be sanctioned.