Volare Shipping Ltd. jumped on its first day of trading in Oslo on Monday after the spin-off arm of Trafigura Group Pte. became the latest in a spree of tanker listings in the Norwegian capital.

Attacks on commercial vessels off the Black Sea’s western coast are on the rise, threatening already-choked trade flows in the region while testing NATO’s readiness to react.

The US blockade of Iran is keeping dozens of laden tankers bottled up along the nation’s coast, while others outside the Persian Gulf are holding off Sri Lanka, according to United Against Nuclear Iran.