A batch of oil tankers that were supposed to load oil from Venezuela have been idling off of the country’s coast for months, offering a headache for some of the traders that got back into the country’s oil trade when sanctions were eased — and a payday for owners of the vessels.

Four supertankers, able of hauling 8 million barrels of oil between them, have been stuck near the Latin American country since December, vessel tracking data compiled by Bloomberg show.  

Two of the ships were hired by Polish oil refiner Orlen SA but for delivery to buyers in Asia, according to lists of charters. The company confirmed in December that its Swiss trading arm had booked at least one ship to carry Venezuelan oil, without naming it. 

Vitol Group, the world’s largest independent oil trader, also has an idle ship on hire near the country’s coast, people familiar with the charter said.

Orlen didn’t respond to requests for comment. Vitol declined to comment.

The delays mean the ships have been racking up millions of dollars of bills without delivering cargo. 

Charterers who book vessels sometimes have to pay a waiting fee called demurrage. For some of the ships near Venezuela, those rates are above $100,000 a day, people familiar with the matter said. It means a three-month delay could cost $9 million.