U.S. Weighs More Penalties on Iran, but Black Market Shows It Can Adapt.

President Obama has vowed to keep the pressure on Iran over its nuclear program after last week's meeting in Geneva, and his advisers said the United States was intensively recruiting other nations to join in a harsher economic embargo against Tehran should diplomacy fail. But as the focus on sanctions intensifies, a review of the United States' experiences in enforcing its own longstanding restrictions on trade with Iran suggests it would be difficult to truly quarantine the Iranian economy. [ABSTRACT FROM PUBLISHER]