
The oil tanker seized by the United States off the coast of Venezuela this week was part of the Venezuelan government’s effort to support Cuba, according to documents and people inside the Venezuelan oil industry.
The tanker, which is called Skipper, left Venezuela on Dec. 4, carrying nearly two million barrels of the country’s heavy crude, according to internal data from Venezuela’s state oil company, known as PDVSA. The ship’s destination was listed as the Cuban port of Matanzas, the data shows.
Two days after its departure, Skipper offloaded a small fraction of its oil, an estimated 50,000 barrels, to another ship, called Neptune 6, which then headed north toward Cuba, according to the shipping data firm Kpler. After the transfer, Skipper headed east, toward Asia, with the vast majority of its oil on board, according to a U.S. official briefed on the matter.
President Nicolás Maduro of Venezuela and his predecessor, Hugo Chávez, have for decades sent oil to Cuba at highly subsidized prices, providing a crucial resource at low cost to the impoverished island.
In return, the Cuban government over the years has sent tens of thousands of medics, sports instructors and, increasingly, security professionals on assignments to Venezuela. That exchange has assumed special importance as Mr. Maduro has leaned on Cuban bodyguards and counterintelligence officers to protect himself against the U.S. military buildup in the Caribbean.

In recent years, however, only a fraction of Venezuelan oil set aside for Cuba has actually reached the island, according to PDVSA documents and tanker tracking data.
Most of the oil allocated for Cuba has instead been resold to China, with the money providing badly needed hard currency for the Cuban government, according to multiple people close to the Venezuelan government.
Some of that money is believed to have been used by Cuban officials to purchase basic goods, though the opacity of the country’s economy makes it difficult to estimate where that money ends up, or how it is spent, or how much goes to business intermediaries with ties to both governments.