President Obama recently signed a law that could essentially prevent Iran, the world's third-biggest oil exporter, from selling oil to many of its usual customers. Europe is preparing to enact its own embargo on Iranian oil. There's wiggle room in terms of how strictly these new rules will be enforced, but if fully enacted, they could devastate Iran's economy, since oil exports bring in about $75 billion per year—nearly 20 percent of Iran's total GDP. They could also push oil prices higher, with gasoline prices cresting $4 per gallon at American filling stations and perhaps even approaching $5.