The first-ever tanker with liquefied natural gas from the United States arrived in Poland on June 8 as part of the country's and the region's efforts to cut its dependence on Russia.
It was the first delivery of U.S. gas to eastern and northern Europe, which is building a new network of energy sources and gas transportation.
Last year, Poland opened its first terminal for liquefied natural gas, or LNG, in Swinoujscie, on the Baltic Sea coast.
Another distant supplier -- Qatar -- has already made some deliveries.
Prime Minister Beata Szydlo said it was a historic moment that improves the region's energy security, as she attended the ceremony welcoming the U.S. tanker "Clean Ocean."
"Today, Poland can say that it is a safe and sovereign country, also because we have such wonderful investments" like the LNG terminal, Szydlo said. "Days like this go down in history."
She urged the United States to develop "further and more efficient cooperation."
The region is trying to cut its reliance on Russia, which has occasionally used its gas exports to exert political pressure. It is planning to bring in gas from the North Sea and also to boost its own production.
The U.S. State Department said in a statement that LNG exports "support American jobs, lower energy prices for our partners abroad, and contribute to Europe's energy security goals using a reliable, market-based supplier."
Officials did not reveal the size of the delivery or the cost of the deal.
The United States is rich in shale gas and has been exporting the fuel to southern European nations such as Spain and Turkey but not yet to nations in the continent's north.
Another U.S. delivery to Poland is expected this summer.
With reporting by the Associated Press