Three days after it collided with another ship off the coast of Shanghai, the tanker Sanchi is still on fire and leaking oil into the East China Sea.

And experts fear that is not even the worst-case scenario.

At least 30 Iranians and two Bangladeshi citizens were aboard the tanker when the collision occurred. One body has been recovered but not publicly identified. Rescue crews said there were no signs of survivors.

Since the crash, the Sanchi has been billowing thick plumes of black smoke into the air. Unless the fire can be brought under control, officials worry that the ship might explode and sink, releasing its 1 million barrels of oil into the water.

The resulting spill would be about three times as big as the Exxon Valdez spill of 1989, one of the worst environmental disasters in history. It would double what the Prestige oil tanker released when it sank off the coast of Spain in 2002. That accident damaged beaches in France, Spain and Portugal, and led to the closure of one of Spain’s richest fishing areas.

Some of the worst spills in history have been even bigger.