Iran is suffering a staggering decline in revenue from its oil exports, and if the trend continues income could virtually disappear by 2015, according to an analysis released Monday by the National Academy of Sciences. Iran's economic woes could make the country unstable and vulnerable, with its oil industry crippled, Roger Stern, an economic geographer at Johns Hopkins University, said in the report and in an interview. Iran earns about $50 billion a year in oil exports. The decline is estimated at 10 to 12 percent annually. In less than five years exports could be halved and then disappear by 2015, Stern predicted.