Imports of Nigerian crude by the United States last week jumped to 559,000 barrels per day, a weekly record going back to mid-2013.

The rise comes as refining firms turned to imports of West African crude that had previously been displaced by domestic grades during the US shale boom.

Nigeria was the fourth largest supplier of foreign crude to the US last week, displacing Mexico and also competing with Iraq and Colombia, according to preliminary figures from the Energy Information Administration, the statistical arm of the US Department of Energy, Reuters reported.

Of the 11 cargos of Nigerian crude that arrived in the US this month, eight went to the East Coast, while the remainder were sent to the US Gulf Coast, according to Thomson Reuters Trade Flows data.

Along with typical cargos of Nigeria’s Qua Iboe, Bonga and Forcados, two 500,000-barrel cargos of Usan medium crude were delivered to Royal Dutch Shell at South Louisiana Port, marking the first time since May 2014 that this crude has entered the US.

From 2004 to 2007, Nigeria exported over one million bpd to the US, but a surge of US domestic production that is of similar quality, including shale oil, later forced African light sweet crude producers, especially Nigeria, to find new destinations for their exports.