The deal the U.S. and Iran are scrambling to reach by the end of March isn't just about nuclear capabilities. It's also about oil. Iran's economy is heavily reliant on oil exports, yet sanctions have crippled the nation's ability to sell its oil on world markets. The country exports just 1.3 million barrels a day now, compared with 2.5 million barrels as recently as mid-2012 when the sanctions were imposed.