Trafigura Group bought seven oil tankers from New York-listed SFL Corp., in the latest example of how trading houses and state energy companies are acquiring vessels to ship crude and products.

Attacks on tankers sailing through the Strait of Hormuz hit their highest last week of any week since the Iran war began, according to maritime security sources tracking incidents, amid a bigger export push by Gulf producers.

Qatar has amassed a fleet of empty liquefied natural gas tankers in the Persian Gulf, a sign that one of the world’s biggest exporters of the fuel may be preparing to boost shipments through the Strait of Hormuz.