A supertanker delivered U.S. crude oil to Spain for the first time in more than six years as Europe increasingly relies on American energy to replace supply disruptions from Russia’s war in Ukraine.

Vessel Solana delivered some of its 2 million barrels of crude into the Spanish port of Bilbao in mid-April before unloading additional oil in Wilhelmshaven, Germany, and Rotterdam, tracking data show. Solana had received its U.S. oil cargo from smaller vessels while in the U.S. Gulf of Mexico before departing for Europe.

Historically, the vast majority of American crude oil shipments to Europe have been done on smaller ships that can carry between 600,000 and 1 million barrels, rather than via the 2-million-barrel supertankers more popular on longer routes, like between the U.S. and Asia. But as European buyers increasingly shun Russian oil following the country’s invasion of Ukraine, U.S. supplies are proving critical to fill the void.

Supertankers will increasingly be “used to send U.S. crude to Europe as the continent’s buyers seek to max out alternatives to Russian oil,” said David Wech, chief economist for analytics firm Vortexa.

Already this year, four supertankers have moved oil between the U.S. and Europe, up from just one during the same period last year, data compiled by Bloomberg show. The arrival of Solana in Spain marks the first supertanker of U.S. crude to make that journey since Washington ended its ban on oil exports in December 2015.

Supertankers have been slowly gaining popularity among European buyers, especially in Rotterdam, a major European oil refining and storage hub. Germany has started to become a key destination, too, after receiving several large shipments in 2020 and 2021. Germany is set to receive its second 2022 supertanker of U.S. oil in May, Vortexa said.