Iran continues to send large amounts of crude oil via the Strait of Hormuz shipping chokepoint, according to TankerTrackers.com, a firm that monitors satellite imagery to observe vessel movements.

Tehran has sent at least 11 million to 12 million barrels through the waterway since the war began on February 28, Samir Madani, the firm’s co-founder said. The actual figure is likely to be higher but there are delays getting satellite feeds because of the conflict, he said.

Oil prices soared to almost $120 a barrel at one stage on March 9 because shipping has largely halted through Hormuz since the conflict started, meaning most producing countries in the Persian Gulf can’t send their supplies to the global market, pressuring their output.

Because Tankertrackers.com inspects satellite imagery, it’s able to capture vessel movements that otherwise go undetected when ships turn off their digital transponders.

A Greek-operated tanker has exited the Persian Gulf via Hormuz with its signal off. It has since reappeared near the coast of India.