More than 6,000 kilometers from Tehran, in treacherous waters off the shores of Singapore, a "dark fleet" of oil tankers waits to offload the precious cargo that helps keep Iran's economy afloat -- a dependency that could also sink it. The fleet has grown steadily over the past five years, delivering Iranian crude to China as the countries work in concert to circumvent international sanctions that target Tehran's lucrative oil exports. But while the clandestine trade has buoyed Iran's budget, it also comes at tremendous cost and risk to Tehran.…
